Amiga ISO Collection/AmigaDemoCD2.iso/ASCII/TEXTE/DOCS/LsdDOCS35.DMS/LsdDOCS35.adf/CourierHSTUser.Manual.pp/CourierHSTUser.Manual

Text File | 1990-09-13 | 172.4 KB | 5,556 lines

                       COURIER HST - USER MANUAL


[De-archived on an Archimedes and fixed by Cygnus of LSD, I removed over 90K
of hard spaces and control codes, if a jobs worth doing...]


USRobotics is a registered trademark and Courier HST is a
trademark of U.S. Robotics, Inc.  Touch-Tone is a trademark of
American Telephone and Telegraph.  InterBridge is a trademark of
Hayes Microcomputer Products, Inc.  MCI Mail is a service mark of
MCI Communications, Inc.  Microcom Networking Protocol (MNP) is a
trademark of Microcom, Inc.  Sprint is a trademark of General
Telephone and Electric.

TABLE OF CONTENTS

Limited Warranty                      vii
FCC Registration Numbers              viii
Connecting to the Telephone Company   viii
Radio and Television Interference     viii
For Canadian Modem Users              ix
How to Use this Manual                x


PART I.  INSTALLATION AND OPERATION

CHAPTER 1 -- Introduction   1-1

Advanced Features
The Courier Product Family
Compatibility


CHAPTER 2 -- Set-Up and Testing2-1

Package Components
Operational Requirements
Assembling the Modem
Testing


CHAPTER 3 -- Operations at a Glance3-1

Data Format
Error Control
Data Compression
Dialing
 HST-Compatible, 9600 bps
 MNP-Compatible, 2400 or 1200 bps
 Non-MNP Compatible, 2400, 1200, 300 bps
Flow Control
Maximum Throughput
High-Speed Channel Turnaround
Link Negotiation
Data Rate Defaults
Nonvolatile Memory (NRAM)
Phone Number Storage
Dialing Stored Numbers
Busy Answer
Inactivity Timer


CHAPTER 4 -- Interface Controls4-1

Terminology
Throughput Guidelines
Error Control
 ARQ Retry Timeout
 Online Data Rate Fallback
 Error Control Modes (&Mn)
   With Auto Answer
 Data Compression Mode (&Kn)
Flow Control
 Transmit Data Flow Control (&Hn)
   Hardware Control
   Software Control
 Received Data Flow Control
   Hardware Control (Rn)
   Software Control (&In)
Data Rate Commands
 Variable Rates
 Fixed Rates
 Maximum Throughput Settings
 DTE Rate Select (&Bn)
 Link Rate Select (&Nn)
DSR Override (&Sn)

CHAPTER 5 -- Internal Controls 5-1

Setting/Using Defaults
 Writing Defaults to NRAM (&W)
 Loading the Factory Defaults (&F)
 Resetting to NRAM Defaults (Z)
 Storing Telephone Numbers (&Zn=s)
Result Codes
 Response Modes (Vn)
 Result Code Sets (Xn)
 Quiet Mode (Qn)
 /ARQ Result Codes
Local Echo
 Command Mode Local Echo (En)
 Online Local Echo (Fn)
The Audio Monitor
 Speaker Control (Mn)
Modem Clock Usage (Kn)
Transmitter Enable/Disable (Cn)
Break Handling (&Yn)
The S-Registers


CHAPTER 6 -- Dialing and Answering 6-1

Basic Requirements
 Transmission Rate
 Error Control
 Automatic Retrain
Placing Calls
 Dial Command (D)
 Dialing Type, X0 or X1 Setting
 Adaptive Dialing, X2-X6 Settings
 Pause (,)
 Dial and Return to Command Mode (;)
 Dialing Letters (")
 Transferring Calls (!)
 Wait for a Second Dial Tone (W)
 Wait for an Answer (@)
 Reversing Originate/Answer Frequencies (R)
Canceling Dialing (any key)
Redialing
 Re-execute the Last Command (A/)
 Automated Redialing (>, A>)
 Continuous Repeat (>)
 Continuous Re-Execute (A>)
 Exiting Repeat Mode
Dialing a Stored Number (DSn)
Escape Code Operations (+++)
 Modem Response to +++
Returning Online (O)
Hanging Up (Hn)
Automatic Answering
 Suppressing Auto Answer
 Points to Remember
International Calls
 U.S./CCITT Answer Tone (Bn)
 Guard Tone (&Gn)
 Pulse Dial Make/Break Ratio (&Pn)


Chapter 7--Queries and Help Screens7-1

User Inquiries (In)
S-Register Query (Sr?)
 S17
 S20
Phone Number Query (&Zn?)
Help Screens
 Basic Command Set ($)
 Extended Command Set (&$)
 Dialing (D$)
 S-Register Functions (S$)


PART II.  REFERENCE

Appendix A--Error/Flow Control Concepts
MNP Level Negotiation
 Throughput
 Level 1
 Level 2
 Level 3
 Level 4
 Level 5
Error Detection/Retransmission
Flow Control
 Example 1--Transmit Data
 Example 2--Received Data


Appendix B--Summaries and Tables  B-1

The RS-232C Interface, with Pin Definitions
Front End Indicators
DIP Switch Summary
Default Settings
S-Register Summary
ASCII Chart


Appendix C--Alphabetical Command Summary C-1


Appendix D--Problems and SolutionsD-1

If You Still Have Problems


Appendix E--Additional Operational InformationE-1

Using Both Voice and Data Communications
High Speed/Low Speed Protocol
Retrain Sequence
PBX, Dedicated Line, and Leased Line Operations
Hewlett Packard Installations
Analog Loopback and Other Tests


Appendix F--Technical Specifications   F-1


Glossary G-1


Index


LIMITED WARRANTY

U.S. Robotics, Inc., warrants to the original consumer or other
end user purchaser that this product is free from defects in
materials or workmanship for a period of two years from the date
of purchase.  During the warranty period, and upon proof of
purchase, the product will be repaired or replaced (with the same
or similar model) at our option, without charge for either parts
or labor.  This warranty shall not apply if the product is
modified, tampered with, misused, or subjected to abnormal
working conditions.
-----------------------------------------------------------------
REPAIR OR REPLACEMENT AS PROVIDED UNDER THIS WARRANTY IS THE
EXCLUSIVE REMEDY OF THE PURCHASER.  THIS WARRANTY IS IN LIEU OF
ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING ANY IMPLIED
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE OR
PURPOSE, AND U.S. ROBOTICS SHALL IN NO EVENT BE LIABLE TO
PURCHASER FOR INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND OR
CHARACTER.
-----------------------------------------------------------------
Some states do not allow the exclusion or limitation of
incidental or consequential damages or allow limitations on how
long an implied warranty lasts, so the above limitations or
exclusion may not apply to you. This warranty gives you specific
legal rights, and you may also have other rights which vary from
state to state.

To obtain service under this warranty, contact the U.S. Robotics
Technical Support Department at 800/982-5151 (in Illinois,
312/982-5151), or by mail at 8100 North McCormick Blvd., Skokie,
Illinois, 60076.  You will be given a Return Materials
Authorization (RMA) number to help us keep track of your warranty
request.  Once you have received your RMA number, take or mail
the product, postage prepaid, to U.S. Robotics at the above
address.  Include proof of the date of purchase.  IMPORTANT:  If
you ship your unit, pack it securely, be sure your RMA number is
visible on the outside of the package, and ship it charges
prepaid and insured.

Should you encounter problems in operating this device,  follow
the instructions in Appendix D in Part II of this manual.  The
Appendix contains solutions to operating problems as well as
procedures to follow if there is an apparent modem malfunction.


FCC REGISTRATION NUMBERS

FCC68:  CJE794-11323-DM-E
RINGER EQUIVALENCE:  0.4B
FCC15:  CJE794FAST


CONNECTING TO THE TELEPHONE COMPANY

It is not necessary to notify the telephone company before
installing the modem.  However, the telephone company may request
the telephone number(s) to which the Courier is connected and the
FCC information printed above.

If the telephone company has any questions or raises problems,
ask them to call the Technical Support Department, USRobotics,
Inc., 800/982-5151 (in Illinois, 312/982-5151).

If the modem is malfunctioning, it may affect the telephone
lines.  In this case, disconnect the modem until the source of
the difficulty is traced.  Do not use the modem on party or coin
telephone lines.

RADIO AND TELEVISION INTERFERENCE

This equipment generates and uses radio frequency energy and if
not installed and used properly, in strict accordance with the
manufacturer's instructions, may cause interference to radio and
television reception.  The Courier HST has been tested and found
to comply with the limits for a Class B computing device in
accordance with the specifications in Subpart J of Part 15 of FCC
rules, which are designed to provide reasonable protection
against such interference in a residential installation.

However, there is no guarantee that interference will not occur
in a particular installation.  If this device does cause
interference to radio or television reception, which you can
determine by monitoring reception when the modem is on and off,
try to correct the problem with one or more of the following
measures.

Reorient the receiving antenna.
Relocate the computer with respect to the receiver.
Relocate the computer and/or the receiver so that they are
on separate branch circuits.

If necessary, consult your dealer or an experienced
radio/television technician for additional suggestions.  You may
find the following booklet, prepared by the Federal
Communications Commission, helpful:


How to Identify and Resolve Radio-TV Interference Problems
Stock No. 004-000-0345-4
U.S. Government Printing Office
Washington, DC 20402


FOR CANADIAN MODEM USERS

The Canadian Department of Communications (DOC) label identifies
certified equipment.  This certification means that the equipment
meets certain telecommunications network protective, operational,
and safety requirements.  The department does not guarantee the
equipment will operate to a user's satisfaction.

Before installing this equipment, make sure you are permitted to
connect it to the facilities of the local telecommunications
company.  You must also install the equipment using an acceptable
method of connection.  In some cases, you may also extend the
company's inside wiring for single line individual service by
means of a certified connector assembly (telephone extension
cord).  You should be aware, however, that compliance with the
above conditions may not prevent degradation of service in some
situations.

Repairs to certified equipment should be made by an authorized
Canadian maintenance facility designated by the supplier.  Any
repairs or alterations made by a user to this equipment, or
equipment malfunctions, may give the telecommunications company
cause to request the user to disconnect the equipment.

For your own protection, make sure that the electrical ground
connections of the power utility, telephone lines, and internal
metallic water pipe system, if present, are connected together.
This precaution may be particularly important in rural areas.

CAUTION:  Do not attempt to make such connections yourself;
contact the appropriate electric inspection authority or
electrician.

   Courier HST Modem Load Number:  38B

The Load Number (LN) assigned to each terminal device denotes the
percentage of the total load to be connected to the telephone
loop used by the device, without overloading.  The  termination
on a loop may consist of any combination of devices, subject only
to the requirement that the total of the Load Numbers of all the
devices not exceed 100.  An alphabetic suffix is also specified
in the Load Number for the appropriate ringing type (A or B), if
applicable.  For example, LN = 38B designates a Load Number of 38
and a B-type ringer.


HOW TO USE THIS MANUAL

This manual is divided into two parts.  The first part is
designed to aid you in getting your modem connected and operating
as quickly as possible.  Part I also includes chapters on command
usage.  Part II contains a number of informative appendixes that
you may or may not need, depending on your situation, plus a
Glossary and Index.

Below is a brief description of the manual's contents.  We
suggest you review at least Chapters 1-3 before operating the
modem.

oChapter 1 -- Introduction

oChapter 2 -- Assembling and testing the modem

oChapter 3 -- Immediate operations -- essentials

oChapter 4 -- Interface controls

oChapter 5 -- Internal controls

oChapter 6 -- Calling, answering and disconnecting

oChapter 7 -- Inquiries and Help screens

The appendixes in Part II cover the following subjects:

oBackground information on error and flow control

oSummaries and tables

oProblems, their causes, and solutions

oAdditional operational information

oTechnical specifications


                  CHAPTER 1 - INTRODUCTION


ADVANCED FEATURES

The USRobotics Courier HST modem represents powerful, advanced
electronic design that gives you optimal speed and accuracy.

Trellis Coded Modulation

Trellis coded modulation is a convolutional coding technique that
makes data transmission less vulnerable to errors caused by phone
network impairments.  It can tolerate twice the telephone channel
noise power as conventional modulation (quadrature amplitude
modulation, or QAM), so there are fewer error-control
retransmissions.  Trellis coded modulation is also less
susceptible to impulse-type noise.

Asymmetrical Modulation

At top speed, data flows in one direction at 9600 bits per second
and at 450 bits per second in the other.  The modems
automatically switch the high-speed channel on demand, i.e.,
depending on which transmitter has the most data to transmit.

In practice, the modems seldom need to reverse channels, since
the asymmetric design reflects typical communications sessions --
brief messages typed at one end of the link, files sent from the
other.  The asymmetrical approach provides the most efficient and
economical strategy for using ordinary phone channels at high
speeds.

Error Control

The MNP protocol is a widely used, sophisticated method of
ensuring data integrity at 2400 and 1200 bps.  A USRobotics
proprietary protocol similar to MNP is used at 9600, 7200 and
4800 bps.  With error detection and retransmission of errored
data blocks, plus flow control, you can be assured that your data
is sent and received with reliability.

Data Compression/Throughput Gains

The Courier HST compresses data to pack more information into
each second of your calls, enabling throughput of up to 19.2K
bits per second.  In addition, the implementation of larger data
blocks eliminates much of the added overhead (protocol
information) associated with less powerful error-control
protocols.

Rate Selection/Flow Control

The Courier HST modem's flow control buffer allows you to set
your computer/modem rate as high as 19.2k bits per second, for
even greater performance. Flow control settings protect
transmissions from data loss.

Online Fallback/Fall Forward

During 9600-bps communications, if severe line impairments
threaten the integrity of data transfer, the modems fall back and
retrain at 7200 bps.  If necessary, they fall back further to
4800 bps.  As line improvements occur, the modems automatically
shift up to the next higher speed.

Programmable Nonvolatile Memory

You can tailor your own default settings for the Courier HST and
store them in nonvolatile random access memory (NRAM).  Each time
the computer is powered on, the modem operates at the settings
you've specified.

Diagnostics

After each call, you can display a Link Diagnostics screen
containing information about the call.  Two S-Registers also
store information on the reason for a call's disconnect.

Shorter Response Time

9600-bps modems are generally most efficient for file transfers.
You'll find that the Courier HST also offers faster response
times during interactive sessions.

THE COURIER PRODUCT FAMILY

In addition to the Courier HST's new features, the modem
incorporates the same popular capabilities of other products in
the USRobotics Courier line:

Link Negotiation Fallback

The Courier HST automatically falls back to 2400, 1200, and 300
bits per second, in both Originate and Answer Modes, to match a
lower rate of a remote modem.  You can optionally set local
interface and link rates at fixed speeds.

Inactivity Timer

You can set the modem to automatically hang up after a specified
number of minutes if there is no activity on the phone line.

Call Duration Reporting

The modem records the duration of your calls in hours, minutes,
and seconds.  This feature enables you to display and print an
audit of your calling activities.  You can optionally use the
modem clock as a real-time clock.


Call Progress Detection

An optional set of result codes (screen messages) lets you know
when a line is busy, a person rather than a modem has answered
the phone, there is no dial tone, or the distant phone is
ringing.

Modem Settings Display

On command, the modem displays its current settings, a handy way
to check your transmission rate, S-registers and other
operational controls.

HELP Screens

You can also display screens that summarize the command sets,
Dial command options, and S-register functions.

Bottom Panel Reference

Operational summaries and other information are printed on the
bottom of the modem case.  A Dual In-Line Package (DIP) switch
guide makes it easy to tailor the switch settings to your
requirements.

Automated Redialing

You can put the modem into Repeat Mode to automatically redial if
a previous dial attempt fails to connect.  This is especially
useful in dialing services whose lines are often busy.

Quote Mode

Set the modem to Quote Mode if you want it to dial an alphabetic
"number," such as 800-"DIAL USR" (USRobotics' Sales Department).

Adaptive Dialing

You can set the modem to first try Touch-Tone dialing.  If tone
dialing doesn't work on the line, the modem automatically
switches to the slower type, pulse (rotary).

Automatic Retraining

Retraining (a resynchronization with the remote modem) occurs if
the modem detects line disturbances that might affect data
reliability.  Retraining occurs at 9600 and 2400 bps.  (Appendix
E-3 contains more information.)


COURIER HST COMPATIBILITY

The Courier HST offers upgrading to 9600 bps while maintaining
compatibility with most installed 2400/1200/300 bps, dial-up
modems and existing software.  Its compatibility features include
the following:

oCan be used with any computer or terminal that is
 compatible with the RS-232C standard interface.

oCan be used with any computer or terminal that uses
 ASCII, the standard character code supported by most
 equipment manufacturers.

oConnects with any modem whose signal scheme is
 compatible with the following standards at the given
 data rate:

   300 bps   Bell 103
   1200 bps  Bell 212A
   2400 bps  V.22bis
   9600 bps  USR-HST

oUses the HST error control protocol at 9600 bps and the
 MNP error control protocol, Service Levels 1-5, at 2400
 and 1200 bps.

oIs fully FCC-certified for the uses described in this
 manual.


                   CHAPTER 2 - SET-UP AND TESTING


Figure 2.1 -- Courier HST


PACKAGE COMPONENTS

The Courier HST package contains the following items in addition
to this manual:

oThe Courier HST modem

oAn RJ11C phone cord

oA power adapter

oA Quick-Reference card, in the manual

oYour warranty card, to be filled out and returned to
 USRobotics, Inc.

OPERATIONAL REQUIREMENTS

The Courier HST has minimal operational requirements.  Be sure to
read the information in the front of this manual about radio and
television interference and connecting to the phone company.  In
addition, you should be aware of the following:

 o   Follow the operating instruction in Appendix E-4 if the
 modem is to be used in either of the following types of
 installation.

 1)   The modem will be installed in a key system PBX in
   which RJ12 or RJ13 jacks are used rather than the
   RJ11 jack.

 2)   The modem will be attached to a user-installed
   phone line or a line leased from the telephone
   company.  Often referred to as dedicated or
   private, this type of line is used for a direct,
   continuous connection between two modems.  The
   connection is made without dialing.

oIf the modem is installed in a Hewlett Packard system,
 be sure to follow the instructions in Appendix E-5.

oIf you're working with a computer rather than a
 terminal, communications software is required to put
 the computer in Terminal Mode.  Some communications
 programs do this automatically when you load the
 program, while others require typing a function key or
 other operation.  If necessary, refer to your
 communications software documentation for instructions.

RS-232C Connector Requirements

You'll need an RS-232C cable to connect the modem to your
computer or terminal.  Use a shielded cable to ensure minimal
interference with radio and television reception.

The modem takes a DB-25P (25-pin plug, or male) connector, but
computer equipment varies.  Check the serial port at the rear of
your machine, labeled MODEM, COMMUNICATIONS, EIA or with a phone
symbol.  (Don't use the port marked PRINTER or AUX.)

The port will be either a socket (female) or plug (male) that
typically accommodates 25 or 9 pins.  For example, the port on
the IBM PC, XT and some compatibles is a plug that takes a DB-25S
(socket) connector.  The port on the IBM AT and some compatibles
is a plug that takes a DB-9S (socket) connector.

NOTE:  Appendix B-1 defines the RS-232C pin assignments required
to operate the modem.  Be sure to check the appendix if you're
not sure what type of 25- or 9-pin connector you need, or if
you're building your own connector.  If your machine has other
than a 25- or 9-pin port, check your documentation to see what
type of RS-232C connector is required.

ASSEMBLING THE MODEM

1.   Turn off the computer or terminal and its peripheral
devices.

2.   Examine the label on the bottom of the modem.  In addition
to the summaries and other information, the label contains
icons to aid in modem assembly.  Check the interfaces at the
back of the modem, shown in the following photograph.

Figure 2.2 -- Interface End, Courier HST


3.   Now review the attached interfaces in Figure 2.3.

   Figure 2.3 -- Connected Courier HST


4.   Check to make sure that the power switch is OFF; press it
towards the zero in the 1/0 icon on the bottom label.  Then
plug the small end of the power supply cord into the power
jack at the back of the modem, and plug the power adapter
into a standard 115-volt AC wall socket.

Disconnect your present phone cable from the wall jack.
Plug one end of the phone cord that came with the modem into
the wall jack, and the other end into the phone jack near
the wall-jack icon.

NOTE:  Older telephone installations may not have the
appropriate modular wall jack and plug.  Adapters and RJ11C
connectors are available from your telephone company or
computer dealer.

If you want to keep your telephone connected for
conventional calls, plug its cord into the jack near the
phone icon.  You can also use both your telephone and modem
in one call, although not at the same time.  Appendix E-1,
Using Both Voice and Data Communications, explains how to
switch control of the phone line between the phone and the
modem.

5.   Next, check the positions of the bank of Dual In-Line
Package (DIP) Switches located at the back of the modem.
These switches are set at the factory to the positions
desired by most users, as shown in Figure 2.4.

Figure 2.4 -- DIP Switch Factory Settings


Use the guide on the bottom of the modem or refer to the
more detailed summary in Appendix B-3 to determine if your
situation requires different settings. If you're connecting
the modem to a dedicated line or to a small interoffice or
PBX system, review Appendix E-4 for special installation and
operating instructions.

6.   The final step is to connect the modem to the computer's or
terminal's serial port with the RS-232C cable described
earlier in this chapter.  Attach the appropriate connectors
to the modem and to the serial port.

NOTE:  When you are using the modem, be sure not to cover the
vents on the top of the case.

The modem is now ready to be tested and operated.

TESTING

To verify that your modem is working properly, follow these
steps:


1.   Turn on your computer or terminal and clear the screen.
Then turn the Courier's power switch ON.  These front
indicator LEDs will light up:

CD  Carrier Detect (if you haven't changed the factory setting of DIP switch 6)
TR  Data Terminal Ready (if you haven't changed the factory setting of DIP
    switch 1)
MR  Modem Ready/Power
RS  Request to Send, if your computer/terminal supports RTS on the RS-232C
    interface
CS  Clear to Send

2.   If you're using a personal computer, load your
telecommunications software and put your computer in
Terminal Mode.  This causes the computer to function as a
terminal rather than a processor:  everything you type at
the keyboard goes directly to the modem.  If necessary,
refer to your communications software documentation for
instructions.

3.   Next, check to see if your machine and modem are
communicating with each other by entering the command to get
the modem's attention.

Type either upper or lower case letters, not a combination.
Enter every command to the modem by pressing the Enter key
(Carriage Return), shown in the example between angle
brackets.  (Don't type the angle brackets.)

Type the following:

 AT <Enter>

If everything is correct, the modem responds as follows:

 OK

NOTE:  The AT command is used alone to check the
modem/terminal interface.  AT is also the mandatory prefix
for all other commands except A/ and A>, used to repeat
execution of the command in the command buffer, and +++, the
escape code.  These exceptions are explained in Chapter 6.

4.   The modem is shipped with DIP switch 4 UP, causing the modem
to display (echo) your keyboard commands.  If your typed
command is not displayed, your local echo is OFF.  To turn
the local echo ON, send the modem the following command.

 ATE1 <Enter>

If double characters appear on the screen, both your modem
and software are set to local echo ON.  Either set your
software to local echo OFF, or turn the modem's echo OFF
with this command:

 ATE0 <Enter>

5.   If no OK appears on your screen, check out the connections
at the interface end of the modem.  Then carefully review
the previous instructions to see if you've missed something.

For information on other testing such as the Analog Loopback
Self-Test, see Appendix E-6.


             CHAPTER 3 - OPERATIONS AT A GLANCE

Here are some brief guidelines for immediate operation of the
modem.

DATA FORMAT

Ten-bit data units:  check the table on page 6-1 or page F-1.

ERROR CONTROL

Both modems must be set to error control mode for error detection
and retransmission to occur.  Always use error control for 9600-
bps communications.

We use the term ARQ (automatic repeat request) for error control.
The three ARQ settings are as follows:

&M0

Normal Mode.  No error control.

&M4

Normal/ARQ Mode -- Default.  The Courier attempts an ARQ
connection; if the signal isn't recognized, the modem continues
in Normal Mode (&M0).

&M5

ARQ Mode.  The Courier attempts an ARQ connection; if the signal
isn't recognized, the modem hangs up.

DATA COMPRESSION

The modem is set at the factory to negotiate for data
compression.  Leave the modem set to its default unless you are
transferring files that are already compressed, in which case you
should disable data compression by setting the modem to &K0.  For
more information, see the throughput guidelines at the beginning
of Chapter 4 and the &K command description in that chapter.

DIALING

Use the following settings/commands to call the specified type of
modem at the indicated speeds.

HST-Compatible, 9600 bps

Terminal/software:  19.2k (preferable) or 9600 bps

Type:  AT &H3 D phone number <Enter>

The command includes the setting for hardware/software flow
control (&H3).  See the flow control guidelines that follow.

If the modem isn't set for error control, include &M4 or &M5 in
the command line.

MNP-Compatible, 2400 or 1200 bps

Terminal/software:  19.2k, 9600, 2400 or 1200 bps

Type: AT &H3 D phone number <Enter>

The command includes the setting for hardware/software flow
control (&H3).  See the flow control guidelines that follow.

Non-MNP Compatible, 2400, 1200 or 300 bps

See the flow control guidelines that follow.

Terminal/software:  2400, 1200 or 300 bps

Type:  AT &M0 D phone number <Enter>

NOTE:  &M0 suppresses the MNP signals that may be misinterpreted
by the remote system and prevent a successful connection.

FLOW CONTROL

Hardware and/or software flow control can be used for transmitted
and received data.   We recommend hardware Transmit data flow
control (&H1) since this setting doesn't affect the data stream.
This is especially important if you're transmitting binary data.

Transmit Data flow control (&H) is required in the following
situations.  Received Data flow control is optional.

oYou're using error control (9600/2400/1200 bps), with
 or without data compression.  Flow control prevents
 buffer overflow in the event that line disturbances
 cause frequent retransmissions.

oThe rate at the local terminal interface is higher than
 the link rate.

oThe volume of data transfer is high.

Flow control commands are explained in Chapter 4.

MAXIMUM THROUGHPUT

Use these settings for both Originate and Answer Modes.  The
default data compression setting, &K1, is assumed.

Terminal/software:  19.2k bps

 Modem:  Fixed terminal interface rate (&B1)
  Variable link rate (&N0)
  Transmit Data flow control (&H1
  preferred, &H2 or &H3)

HIGH-SPEED CHANNEL TURNAROUND

As described in Chapter 1, HST modems use asymmetrical
modulation.  The modems allocate the high-speed channel on demand
so that the modem with the greatest amount of data in its buffer
transmits at 9600 bps.

Turnaround of the channel is automatic and requires no user
intervention.  If the remote modem has a 300-bps back channel,
the Courier automatically drops its back channel rate from 450 to
300 bps.

LINK NEGOTIATION

When a Courier HST calls an HST-compatible modem and both are
operating at 9600 bps, the modems negotiate the link connection
(shake hands) at 2400 bps and automatically resume operation at
9600 bps.  The lower handshaking rate maintains compatibility
with the existing telephone network as well as existing hardware
and software.

It's possible for two HST-compatible modems to connect directly
at 9600, without 2400-bps handshaking, but both modems must be
set as follows:

Terminal/software:  9600 or 19.2k bps
 Modem:  Fixed link rate of 9600 bps (&N6)
  Error control, either &M4 or &M5
  Transmit Data flow control, preferably
  hardware, &H1

DATA RATE DEFAULTS

   Terminal interface:  &B0, detect rate from the AT command,
  then follow the connection rate.
   Link interface:  &N0, negotiate the highest possible
  rate with the remote modem in both
  Originate and Answer Modes.

The terminal interface and link rates may be set to fixed rates
using &B1 or &N1-6, respectively.

NONVOLATILE MEMORY (NRAM)

The modem is factory set (DIP switch 10 OFF) to load the settings
stored in NRAM on power up.  Write your own configuration
defaults to NRAM with the &W command.  To review the NRAM
settings, refer to Appendix B-4 or send the modem the I5 option
of the Inquiry command:

 ATI5 <Enter>

PHONE NUMBER STORAGE

Use &Zn=s to store four frequently called phone numbers in NRAM
(nonvolatile memory); n = positions 0 through 3, s = the number-
string.  The string may contain a maximum of 36 characters and
any Dial command options, but no other operational settings.

Example:  AT&Z=9,,1 312 5551234 <Enter> (Store at position 0)

Example:  AT&Z1=5551234 <Enter> (Store at position 1)

DIALING STORED NUMBERS

To dial, issue the DSn command, where n indicates the position of
the number in NRAM.

Example:  ATDS1 <Enter>  (Dial number at position 1)

The first command in the following sequence stores the phone
number and access code for a long distance service.  The second
command dials the stored number/access code and continues dialing
the long distance phone number.

 AT&Z2 = 5551234,,9876,, <Enter>
 ATDS2 D 1 312 5556789 <Enter>

BUSY ANSWER

Use A> instead of A/ and the modem redials up to 10 tries instead
of once.  Neither A> nor A/ takes the AT prefix or a Carriage
Return.

Insert the Repeat Mode command (>) before or after the Dial
string and the modem automatically redials up to 10 tries:

 AT>D5551234 <Enter>
 ATD5551234> <Enter>

You may include the Repeat command when you store a phone number-
string in NRAM:

 AT&Z2=5551234> <Enter>

INACTIVITY TIMER

Set the inactivity timer (S-Register 19) if you suspect that a
connection may be inadvertently left open without data transfer.


                 CHAPTER 4 - INTERFACE CONTROLS

Use the commands explained in this chapter to select the modem's
operating characteristics at the terminal and link interfaces.
The commands apply to error and flow control, and to the speed-
select options at both interfaces.  For background information on
these features, see Appendix A.

NOTE:  When you change a setting during a session, the modem
retains that setting until you do one of the following:

oSelect a new setting.

oIssue the ATZ command to reset the modem to its
 software defaults.  If DIP switch 10 is OFF, the modem
 resets to the defaults stored in nonvolatile memory
 (NRAM).  If DIP switch 10 is ON, the modem resets to
 the factory settings stored in read-only memory (ROM).

 Issuing the AT&F command resets the modem to its
 factory settings.

oTurn the modem off.

TERMINOLOGY

For simplicity, references to a terminal in this chapter mean
both conventional terminals and microcomputers.

ARQ (automatic repeat request, i.e. retransmission) is the term
used by USRobotics in error control commands and response codes.

In summaries, the terminal is referred to as DTE (Data Terminal
Equipment), while the modem is referred to as DCE (Data
Communications Eqipment).  DTE/DCE indicates the terminal/modem
interface.

THROUGHPUT GUIDELINES

The following guidelines should help you to make the most of the
Courier HST modem's advanced performance features.  In many
instances, experimentation and experience will indicate what
works best for your applications.

1.   You'll attain optimal throughput under the following
conditions:

oYour communications software allows fixing the DTE rate
 higher than the link rate, e.g., setting the
 terminal/software to 19.2K bps and setting the modem to
 &B1.

 If your software automatically switches bit rates to
 follow the connection (link) rate (9600, 2400, 1200 or
 300 bps), the modem must be set to &B0 for a variable
 DTE rate, and your throughput will be reduced.

oThe call is under error control Service Levels 3
 through 5, which includes data compression.  See
 Appendix A for comparative throughput information on
 each successive level.

oThroughput is slightly higher for text files than for
 binary files such as .EXE or .COM files.  For a
 comparative table, see Appendix A.

2.   Files that are already compressed become larger when
subjected to further data compression.  An example is the
.ARC files downloaded from many BBS's.  Another is random 8-
bit binary files, which appear to the modem to be
compressed.  To avoid a decrease in throughput when
transferrring these and similar files, we recommend
disabling data compression (&K0).

3.   Many non-text files require a file transfer protocol, with
varying throughput results.  For example, certain public
domain file transfer protocols have the following effects:

XMODEMThroughput is severely reduced, regardless of the
   Courier's performance features, due to XMODEM's
   short block lengths (128 bytes) and overhead
   (error control protocol information).

YMODEMThere is an improvement over XMODEM, due to larger
   block lengths (1k bytes), but throughput is still
   reduced by the protocol's error control overhead.

YMODEM-G and ZMODEM are better choices, YMODEM-G being the
most efficient.  These protocols assume the modems are
handling error control:  overhead is minimal, with
throughput almost equal to throughput with no file transfer
protocol.

ERROR CONTROL

While error control is optional, it should always be selected for
9600 bps sessions.  The error control protocol uses cyclic
redundancy checking for error detection, and an automatic repeat
request (ARQ) for retransmission of errored data blocks (or
frames).

ARQ Retry Timeout

It may happen that a retransmission request for the same frame
occurs repeatedly.  Ordinarily this is due to a serious
disturbance in the phone connection.  The retry maximum is 12,
after which the modems automatically hang up instead of running
up wasteful phone charges.  If the Courier hangs up and you don't
know why, query register S20 with this command:

 ATS20? <Enter>

If a code of 6 is returned, the modems reached the retry timeout
and hung up.  Place the call again; you'll more than likely get a
better connection.

Online Data Rate Fallback

On 9600-bps MNP connections, to help avoid an automatic
disconnect due to a retry timeout, the modems automatically fall
back to 7200 bps.  If necessary, they fall back again to 4800
bps.  As soon as they sense line improvements, the modems shift
back up to the next higher speed.

Online fallback is designed to keep you online at high speeds
despite phone line impairments.  This feature has the following
characteristics:

oOnline fallback has no effect on the DTE rate set with
 the &B command.

oThe link rate must be set to &N0 (variable rates).  If
 set to 9600 bps (&N6), the modem remains fixed at that
 rate.  A setting of 7200 bps (&N5) or 4800 bps (&N4)
 disables online fallback.

oDuring retraining down to the next lower speed, the
 Modem Ready LED flashes.  In all other ways, the
 fallback is transparent to users.

oThe modem does not send result codes reflecting the
 rate changes.

oOnline fallback is distinct from the link negotiation
 fallback that makes the Courier HST compatible with
 most 300/1200/2400-bps modems.

Error Control Modes (&Mn)

Under error control, the calling modem includes an error control
request in its link negotiation signals.  The answering modem may
or may not recognize the request.

NOTE:  Error control requires Transmit Data flow control,
preferably the &H1 setting.

&M0

Normal Courier Mode, no error control.  Use this setting if
you're calling a non-MNP modem (2400/1200/300 bps), as the error
control request may be misinterpreted by the remote system and
prevent a connection.  Don't use this setting for 9600-bps calls.

&M1-3

These options are reserved for future use.

&M4

Normal/ARQ Mode.  Default.  If the remote modem doesn't recognize
the Courier's error-control request, the Courier automatically
operates in Normal Mode (&M0).  Use this adaptive mode if error
control isn't crucial.

&M5

ARQ Mode.  If the remote modem doesn't recognize the error-
control request, the Courier HST hangs up.  Use this setting if
error control is an absolute requirement.

With Auto Answer

To use error control for incoming calls, set the modem for Auto
Answer and for either &M4 or &M5.  When calls come in, the
Courier HST goes off hook and responds to an error-control
request if one is sent.  If the Courier doesn't receive a request
and is set to Normal/ARQ Mode (&M4), it answers the call in
Normal Mode.  If it doesn't receive a request and is set to ARQ
Mode (&M5), it hangs up.

Data Compression Mode (&Kn)

Data compression is implemented through Level 5 of the error
control protocol, and only occurs if the modems can establish an
ARQ connection.  In addition to the obvious benefits to file
transfer, compression speeds up interactive applications by
filling the screen more quickly.  (Appendix A describes the ARQ-
connection sequence at all five protocol levels and includes a
comparative table for different types of compressed files.)

NOTE:  The modem should also be set for Transmit Data flow
control, preferably &H1.

&K0

Data compression is disabled.  Some files should not be
compressed and require this setting.  See the throughput
guidelines at the beginning of this chapter.

&K1

Auto enable/disable.  Default.  The Courier enables data
compression only if the DTE rate setting (&B) is higher than the
link rate (&N).  If the rates are the same, the application of
the compression algorithm may actually reduce throughput, to your
disadvantage.  If the remote modem doesn't recognize the request
for compression, the ARQ connection proceeds at the last
negotiated protocol level.

&K2

Data compression is enabled.  Use this setting if you don't want
the modem to automatically disable compression.  If the remote
modem doesn't recognize the request for compression, the ARQ
connection proceeds at the last negotiated protocol level.

FLOW CONTROL

This feature controls the flow of data into and out of the
modem's Transmit and Receive data buffers, and is used for both
error controlled and normal connections.  Due to differing user
equipment requirements, however, the Courier is shipped with all
flow control options disabled.

Users at Hewlett Packard installations using the ENQ/ACK protocol
should note the HP settings, &I3 and &I4, described under
Received Data Software Control (&In).

NOTE:  Flow control of data from the DTE to the modem is required
under the circumstances described under Transmit Data Flow
Control (&Hn).  Received Data flow control is not as critical
unless, for example, you are writing incoming files to disk on a
slow computer.  For information on flow control concepts, refer
to Appendix A.


Transmit Data Buffer Sizes

The size of the Transmit data buffer depends on whether the
connection is under error control or not, as follows.

oARQ connections:  3.5k bytes.

oNon-ARQ connections:  1.5k bytes, allowing error
 control file transfer protocols such as XMODEM and
 YMODEM to be used without flow control.

 If bit 3 of S-register 15 is turned on, the non-ARQ
 buffer size is reduced to 128 bytes, for the
 convenience of some remote users of slower modems.  See
 S15 in Appendix B-5.

Received Data Buffer Size

The size of this buffer remains constant at 2k bytes.

Transmit Data Flow Control (&Hn)

This type of flow control is for data transmitted by the terminal
to the modem.  The modem monitors its buffer as data comes from
the terminal.  If the buffer approaches 90% capacity, the modem
signals the terminal to stop sending.  When the modem has sent
enough data over the link to half empty the buffer, it signals
the terminal to resume transmitting.

When it is Required

Transmit Data flow control should be enabled in the following
situations:

oYou're using error control (9600/2400/1200 bps), with
 or without data compression.

oThe rate at the terminal interface is higher than the
 link rate, e.g., the terminal's sending at 19.2k bps
 and the link rate is 9600 bps.

oThe volume of data transfer is high.

Hardware Control

The modem lowers the Clear to Send (CTS) signal on the RS-232C
interface (Pin 5) when its buffer nears 90% capacity.  The modem
raises CTS when the buffer is about half full.

NOTE:  If your terminal and communications software support CTS,
use hardware control as it is more efficient and doesn't affect
the data stream.

Warning

If you are using an XMODEM-type protocol to transfer binary
files, always use hardware flow control.  If your system doesn't
support CTS, disable flow control, and be sure the terminal and
link rates are equal by setting the modem to &B0 and &N0.

Software Control

The modem sends the conventional ASCII Transmit on/off (XON/XOFF)
characters, depending on how full the buffer is, as follows:

XON <Ctrl>-Q(ASCII 17 Decimal, 11 Hex)
XOFF<Ctrl>-S(ASCII 19 Decimal, 13 Hex)

The ASCII characters may be user-defined;  see S-registers S22
and S23 in Appendix B-5 and the ASCII chart in Appendix B-6 or on
the Quick-Reference card.

&H0

Transmit Data flow control disabled.  Default.

&H1

Hardware flow control.  Recommended setting.  Requires that your
terminal and software support CTS.  If your software requires,
turn off XON/XOFF signaling.

&H2

Software flow control.  Requires that your software support
XON/XOFF signaling.

&H3

Use both hardware and software flow control.  If you are unsure
about what your equipment supports, select this option.

Received Data Flow Control

Separate commands, &Rn (hardware) and &In (software), control the
flow of Received Data passed by the Courier to your DTE. If the
data rate at the DTE interface is 9600 or 19.2k bps, there may be
a need at times to signal the modem to temporarily stop passing
data, for example, to read what's on the screen.


Hardware Control (&Rn)

If your terminal and software support Request to Send (RTS) on
the RS-232C interface (Pin 4) and RTS is not always high, the
terminal lowers RTS to signal the modem to stop passing it
received data, and raises RTS when it is ready to receive.

&R0

Reserved.

&R1

Ignore RTS.  Default.  This setting is required if your terminal
does not support RTS.

&R2

Hardware flow control of received data enabled.  The modem only
sends data to the terminal when RTS is high.

Software Control (&In)

Use of this feature requires that your software support XON/XOFF
signaling (<Ctrl>-Q and <Ctrl>-S, respectively).

Warning

When software flow control is enabled, the modem looks for
<Ctrl>-S or <Ctrl>-Q characters.  If these characters occur in a
file, they will be misinterpreted as flow control characters.  We
recommend that, if possible, you select hardware flow control
instead.

NOTE:  Because of the risk described above, recommended settings
given below are only provided for those users who cannot use
hardware flow control.

&I0

Disable XON/XOFF flow control of received data.  Default.
Recommended for non-ARQ (Normal Mode) calls, but see &I5.  This
option makes all characters, including control characters,
transparent to the modem.

&I1

The Courier acts on your typed XON/XOFF signals, and passes them
to the remote computer.  Use in ARQ Mode only, but keep in mind
that the XON/XOFF signals sent to the remote computer may
interfere with XON/XOFF signaling occurring at the remote
computer/modem interface.  See &I2.

&I2

The Courier acts on your XON/XOFF signals, but removes them from
the data stream instead of passing them to the remote computer.
This ensures that the remote computer does not confuse your
XON/XOFF signals with those from its attached modem.  This is the
recommended setting for ARQ Mode.

However, if the call is not under error control, there is no flow
control on the phone link.  If you send an XOFF to your modem and
it stops passing on data, there is no way to tell the remote
computer and modem to stop sending, and your modem's buffer may
overflow.  For more reliable control in non-ARQ Mode, see &I5.

&I3

Hewlett Packard protocol--Host Mode.  Applies only to modems
attached to an HP mainframe.  See Appendix E-5.

&I4

Hewlett Packard protocol--Terminal Mode.  Applies only to modems
attached to terminals in an HP system.  See Appendix E-5.

&I5

This setting is particularly designed to enable flow control on
the phone link when the connection is not under error control.

At &I5, a Courier in ARQ Mode operates the same as it does when
set to &I2.  It acts on your XON/XOFF signals but doesn't pass
them to the remote system.  The error control protocol enables
the modems to control the flow of data on the phone link.

In non-ARQ Mode, a Courier set to &I5 operates as though flow
control were disabled (&I0) in respect to the local DTE
interface.  However, it looks to the phone line for incoming
XON/XOFF signals.  When the remote operator sends XON/XOFF
signals, the Courier either resumes or stops transmitting data
over the link and drops the signals from the data stream.

If both modems are set to &I5, operators at each end can signal
the remote modem to stop sending, thereby controllling the data
flow on the phone link and preventing their own modem's buffer
from overflowing.  At the DTE/DCE interfaces, the modems
independently control the flow of data through their Transmit
Data (&H) settings.


DATA RATE COMMANDS

These commands allow you to select variable or fixed data rates
at the DTE and link (modem-to-modem) interfaces.  The highest
possible rate at the DTE interface is 19.2k bps; the highest
possible rate at the link interface is 9600 bps.


Variable Rates

At the modem's default settings (&B0, &N0) the rates at the DTE
and link interfaces are the same and vary with each call, as
follows:

oInitially the modem detects its rate from the rate at
 which the terminal sends it the AT command.  That rate
 is determined by the terminal or software setting.

oWhen originating or answering a call, the Courier and
 the remote modem negotiate the highest possible link
 rate.  For example, if the terminal sends the AT
 command at 9600 bps and the Courier calls a modem
 operating at 1200 bps, the Courier automatically falls
 back to 1200 bps.  The Courier notifies the terminal of
 the adjustment by sending the result code CONNECT 1200.

 The Courier readjusts to the rate of the next AT
 command or, if auto answering a call, readjusts to the
 rate of the remote modem.  See Appendix E-2 for more
 details.

NOTE:  If your software switches its rate to match the connection
rate, reset the software for a higher speed call before dialing
again.  For example, if your modem and software dropped back to a
lower rate for the last call and you want to make a high-speed
call, first reset the software.  Otherwise your Dial command is
sent at the previous rate, and the remote 9600-bps modem drops
back to match your lower rate.

Fixed Rates

If your software supports fixed rates, you can fix the rate at
either the terminal or link interface, or both.  These settings
apply to both normal and error-control operations, but be sure to
enable Transmit Data (&H) flow control.

Maximum Throughput Settings

For the greatest throughput, recommended settings (assuming
software allows fixing the DTE rate) are as follows:

Terminal/software:  19.2k bps (&B7)
 Modem:  Fixed DTE rate (&B1)
  Variable link rate (&N0)
  Data compression (&K1)
  Transmit Data flow control (&H1, 2 or 3)


DTE Rate Select (&Bn)

Use this command to select variable or fixed rates at the
terminal interface.

&B0  Variable rates.  Default.  The terminal interface rate
follows the connection rate.  Requires &N0 for the link
rate:  the modem automatically adjusts to the rate of the
remote modem.

&B1  Fixed rate:  requires software support of this feature.
Allowable terminal/software settings are 19200, 9600, 7200,
4800, 2400, 1200, 300 bps.  Setting the terminal to 19.2k
bps enables the greatest throughput.

Link Rate Select (&Nn)

&N0  Variable operations.  Default.  The link rate varies
according to the modems' connection sequence.

&N1-6  Fixed link rate:  the modem only connects if the remote
modem is also operating at the same rate.  The setting may
be lower than or equal to the &B setting.  If lower than the
&B setting, enable Transmit Data (&H) flow control to
prevent the possibility of data loss.  Allowable rates are
as follows:

&N1  300 bps  &N4  4800 bps
&N2  1200 bps &N5  7200 bps
&N3  2400 bps &N6  9600 bps

If you wish, you can filter out calls at other than a
specific speed, for security or other reasons, by fixing the
link rate.

DSR OVERRIDE (&Sn)

The Data Set Ready (DSR) function (Pin 6 on the RS-232C
interface) is required on some systems to enable the modem to
signal the terminal when the modem is ready to answer a call.
Typically, DSR signaling is overridden.

&S0  DSR is always ON (override).  Default.

&S1  The modem controls DSR.


                    CHAPTER 5 - INTERNAL CONTROLS

The commands explained in this chapter are of two types.  The
first group concerns default configurations, for example, writing
your own power-on defaults to nonvolatile random access memory
(NRAM).  The remaining commands are used to select the modem's
local operating characteristics, for a current session or to
include in your default configuration.  They include result code,
echoing, and other options.

NOTE:  When you change a default setting during a session, the
modem retains that setting until you do one of the following:

oSelect a new setting.

oIssue the ATZ command to reset the modem to its
 software defaults.  If DIP switch 10 is OFF, the modem
 resets to the defaults stored in nonvolatile memory
 (NRAM).  If DIP switch 10 is ON, the modem resets to
 the factory settings stored in read-only memory (ROM).

 Issuing the AT&F command resets the modem to its
 factory settings.

oTurn the modem off.

SETTING/USING DEFAULTS

The Courier HST is shipped from the factory with its software
defaults stored in read only memory (ROM) and also in
programmable nonvolatile random access memory (NRAM).  The
inclusion of NRAM allows you to program your own configuration
and save the settings as your power-on defaults.

Writing Defaults to NRAM (&W)

If you store your own default software settings in NRAM, the
Courier loads those settings when it is powered on if DIP switch
10 is UP (factory setting).

A list of the settings stored in NRAM is in Appendix B-4.  You
can also display the settings at any time by selecting option 5
of the I (inquiry) command:

 ATI5 <Enter>

If you've sent the modem commands to change settings throughout
your session and want to save your current configuration, issue
the &W command:

 AT&W <Enter>

You can also specify your configuration in a single command
string that includes the &W command, as in this example:

 AT X4 &B1 &M5 &H1 &I1 M3 &W <Enter>

Modify one or several settings at any time, for example:

 AT X7 &W <Enter>

Loading the Factory Defaults (&F)

Factory defaults are permanently stored in read only memory
(ROM).  They are listed in the table of NRAM settings in Appendix
B-4.  You can set the modem to its factory defaults during any
session by typing:

 AT&F <Enter>

If DIP switch 10 is DOWN, the factory settings are loaded at
power on instead of the NRAM defaults.

Resetting to NRAM Defaults (Z)

If DIP switch 10 is UP, reset the modem to its NRAM defaults by
typing the following command:

 ATZ <Enter>

NOTE:  On reset, the modem also checks the status of DIP switches
2-5 and 9:  if you change the setting of any of these switches
when the modem is on, use the Z command to initiate the new
setting(s).

Storing Telephone Numbers (&Zn=s)

The modem stores up to four frequently called phone numbers.
Write the numbers to NRAM with the &Zn=s command, where n is
position 0 through 3, and s is the number-string.

The number-string may be up to 36 characters long, including any
Dial command options.  The following example includes the tone-
dial (T) and comma pause options of the Dial command.  The number
is stored at position 0, assumed because there is no n parameter.

 AT&Z=T9,,5551234 <Enter>

The next example stores the phone number and user's access code
for a long distance phone service.

 AT&Z1=5551234,,9876,, <Enter>

Dial the stored number using the DSn command, for example, DS2
<cr>.  Additional examples are in Chapter 6.

NOTE:  Don't include modem settings in the &Z string.  If the
call requires a special setting, insert the appropriate command
when you dial the stored number.  In the following example, &M0
(no error control) is substituted for the user's error control
default setting:

 AT&M0DS2 <Enter>

Then reset the error control mode after the call, for example:

 AT&M4 <Enter>

RESULT CODES

Four commands control the result codes the modem returns to the
screen:

Vn   Numeric/verbal response mode
Xn   Result code subset
Qn   Display/suppress all result codes
&An  Display/suppress /ARQ result codes

Response Modes (Vn)

Result codes are sent to the screen in either words (Verbal Mode)
or numbers (Numeric Mode).  The Courier is factory set to verbal
messages when it is powered on (DIP switch 2 is UP).  Use the V
command to select verbal/numeric result codes independently of
the switch setting.

V0   Numeric Mode.  Numeric result codes are followed by a
Carriage Return but no Line Feed, as in the following
example, where a 3 is returned (for NO CARRIER).

 ATD1234567 <Enter>
becomes
 3TD1234567 <Enter>

V1   Verbal Mode.  Verbal responses are preceded and followed by
a Carriage Return and a Line Feed, as in the following
example:

 ATD1234567 <Enter>
 NO CARRIER

Result Code Sets

The format of the command to select a result code set is ATXn,
where n is a value from 0 through 7:

X0   Basic subset, returns the first five codes (0-4) in the
following table.

X1   Extended subset, codes 0-5, 10 and 13.  Default.  This set
adds rate-specific CONNECT messages to the Basic set.

X2-7 These options offer advanced call-progress codes and
functions.

                    RESULT CODES OPTIONS TABLE

                                               Commands
                                    X0  X1  X2  X3  X4  X5  X6  X7
       Result Codes
        0/OK                         X   X   X   X   X   X   X   X
        1/CONNECT                    X   X   X   X   X   X   X   X
        2/RING                       X   X   X   X   X   X   X   X
        3/NO CARRIER                 X   X   X   X   X   X   X   X
        4/ERROR                      X   X   X   X   X   X   X   X
        5/CONNECT 1200                   X   X   X   X   X   X   X
        6/NO DIAL TONE                       X       X       X   X
        7/BUSY                                   X   X   X   X   X
        8/NO ANSWER                              X   X   X   X   X
        9/Reserved for future use
       10/CONNECT 2400                   X   X   X   X   X   X   X
       11/RINGING                                        X   X   X
       12/VOICE                                          X   X
       13/CONNECT 9600                   X   X   X   X   X   X   X

    FUNCTIONS
       Adaptive Dialing                      X   X   X   X   X   X
       Wait for 2nd Dial Tone (W)                X   X   X   X   X
       Wait for Answer (@)                       X   X   X   X   X
       Fast Dial                             X       X       X   X


Options Summary

1.   An additional group of CONNECT messages (15-17) indicates an
error-control connection with an HST- or MNP-compatible
modem.  See /ARQ Result Codes (&An) later in this section.

2.   Adaptive dialing causes the modem to automatically use
Touch-Tone dialing and, if that doesn't work on the line,
revert to pulse dialing.

3.   W and @ are Dial options described in Chapter 6.

4.   Fast dial causes the modem to dial as soon as a dial tone is
detected, rather than wait the normal two  seconds.  If
there is no dial tone, the modem times out after 5 seconds
and sends the NO DIAL TONE (6) result.

5.   After sending the BUSY (7) result code, the modem hangs up.

6.   The NO ANSWER (8) result code is returned, instead of the
standard NO CARRIER, when the @ option is used and there is
no answer at the remote end.

7.   After sending the VOICE (12) result code, indicating a voice
answer, the modem hangs up.

8.   X6 implements all result codes and functions.  X7 includes
all of X6 except the VOICE (12) result.

Quiet Mode (Qn)

Enable/suppress the display of result codes.  The Courier is
shipped with DIP switch 3 DOWN and defaults to display ON when
the modem is powered on. The commands here control the display
independently of the switch setting.

Q0   Result codes are displayed.

Q1   Result codes are suppressed (made quiet).  This is useful
when the messages might interfere with the data stream.

/ARQ Result Codes (&An)

If these codes are enabled, one of the following results is sent
to the screen when a successful HST or MNP connection is
established.  (A setting of X1 or higher is assumed.)

(15) CONNECT 1200/ARQ
(16) CONNECT 2400/ARQ
(17) CONNECT 9600/ARQ

&A0  /ARQ codes are disabled.  If your software does not allow
the /ARQ result codes, use this setting.  Suppression of the
/ARQ codes doesn't affect the error control protocol; the
modem returns the standard CONNECT messages.

&A1  /ARQ codes are displayed. Default.

LOCAL ECHO

Two commands control what the modem displays on the screen.  The
En command applies to when the modem is in Command Mode.  The Fn
command applies to when the modem is online to another system.

Command Mode Local Echo (En)

The En command enables/disables the display of your typed
commands.  If double characters appear on the screen, both the
modem's local echo and the software's local echo are on.  The
Courier is shipped with DIP switch 4 UP, for local echo ON when
the modem is powered on.  The commands here control the echo
independently of the switch setting.

E0   Command Mode echo OFF.  The modem does not display keyboard
commands.

E1   Command Mode echo ON.

Online Local Echo (Fn)

This command causes the modem to display a copy of the data it is
transmitting to another system.  Many systems, however, return a
copy of received data, which is called a remote echo.  If the
modem's online echo is ON and there is remote echoing, double
characters appear on the screen.

In some microcomputer documentation the online echo setting is
called the "Duplex" setting, although the term is not technically
accurate.

F0   Online echo ON.  Sometimes called Half Duplex.  As the modem
transmits data to a remote system, it also sends a copy of
the data to the screen.

F1   Online echo OFF.  Sometimes called Full Duplex.  This is the
default.

THE AUDIO MONITOR

The modem's speaker enables you to monitor the dial-connect
process.  There are several ways to make use of this feature.
After the Courier 2400 dials a number, it waits 30 seconds for a
high-pitched answer tone from the other modem, immediately
followed by data signals, called a carrier.  These signals must
occur before a data link is established.

If someone answers the phone, or if the line is busy, the modem
sends the message NO CARRIER to your screen after 30 seconds.  If
you listen to the speaker, you can respond immediately instead of
waiting for the modem to time out.

For example, if you hear someone answering the call, you might
pick up the phone and talk to the person or cancel the call by
pressing any key on the keyboard.  In the same way, you can
cancel a call when you hear a busy signal.

You can also hear if dialing is proceeding too fast for the
system.  Terminate the call (press any key) and reenter the Dial
command with a comma or two to allow more time.  This applies to
accessing an outside line (dialing 9, for example) as well as to
checking out whether a public service has enough time to respond
to your account number or other code.

Speaker Control (Mn)

You can disable the speaker entirely or set the speaker to
monitor different segments of the dial-connect sequence.

M0   The command ATM0 turns the speaker OFF entirely so that you
don't hear the modem go off hook, dial, etc.

M1   The speaker is ON until Carrier Detect.  Default.  You can
monitor call progress until the Courier detects the remote
modem's carrier signals, or until the 30-second timeout and
result code display.  At Carrier Detect, the modem
disconnects the speaker and data transmission sounds are
suppressed.

M2   The speaker is ON continuously, including during data
transmission.

M3   The speaker doesn't go ON until after the last digit is
dialed, then goes OFF at Carrier Detect.

MODEM CLOCK USAGE (Kn)

The modem clock is used as a call-duration timer or as a real-
time clock.  Used in conjunction with the In (Inquiry) command,
the modem returns the duration of the last call in hours,
minutes, and seconds or the actual time.

K0   Call-Duration Mode.  Default.  The modem times each call
from CONNECT to NO CARRIER, and stores the information until
the next connection or the modem is reset.  At ATI3 <cr>,
the modem displays the call's duration.  If you wish, you
can maintain a call log by printing this information after
each call.

K1   Real-Time Mode,  The clock operates as a real-time clock
regardless of the presence of a carrier.  Set the clock
(military time) by specifying the hour, minutes, and seconds
as in the following example, which sets the clock at the
real time of 1:30 p.m.

 ATI3=13:30:00 K1 <Enter>

At ATI3, the modem displays the real time.  You'll need to
set the clock each time you power on the modem, but the
clock is not affected by the reset command, ATZ.

TRANSMITTER ENABLE/DISABLE (Cn)

If an additional terminal and modem share the phone line for
monitoring purposes, the second modem is placed in Receive Only
state by disabling its transmitter.

C0   Transmitter disabled.  Modem is set to Receive Only.

C1   Transmitter enabled.  Default.

BREAK HANDLING (&Yn)

The Courier HST allows you to send a break to abort data transfer
without disconnecting from the data link.  The following options
are available.

NOTE:  A destructive Break to the modem resets its data
compression tables.  The remote modem also resets its data
compression tables.

&Y0  Destructive, no Break transmitted:  the modem clears the
data from its transmit buffer (all data is lost) but does
not pass on the Break to the remote modem.

&Y1  Destructive, expedited:  the modem clears the buffer and
immediately sends a Break to the remote modem.  This is the
default setting.

&Y2  Nondestructive, expedited:  the modem retains buffer data,
but immediately sends a Break to the remote modem.

&Y3  Nondestructive, unexpedited (send Break in sequence):  the
modem transmits any buffer data received before the Break,
sends the Break, and then sends any subsequent input from
the computer or terminal.

THE S-REGISTERS

The S-Registers are used to set various timing parameters and
other operations, including redefinition of selected ASCII
characters.  The defaults typify the requirements of most users.

A detailed summary of the S-Register functions is in Appendix B-
5.  Less detailed summaries are on the bottom label of the modem
case and in the Quick-Reference card.


               CHAPTER 6 - DIALING AND ANSWERING

BASIC REQUIREMENTS

To successfully establish a communications link, the called or
calling modem must be compatible with the following standards at
the specified rates.

 Bits per
Second   Standard

9600USR-HST or compatible
2400CCITT V.22bis
1200Bell 212A
 300Bell 103

To successfully exchange data, both modems must use the same 10-
bit data format.  The formats allowed are as follows:

                    Start     Data                     Stop
                    Bits      Bits      Parity         Bits
                     1         7      Even, Odd,        1
                                      Mark, Space
                     1         7      None, Even, Odd,  2
                                      Mark, Space
                     1         8      None             1,2


Transmission Rate

In general, you should know the transmission rate of the other
modem before calling.  However, if the link rate is set to the
default, &N0, and the remote modem is operating at a lower rate,
the Courier falls back to the rate of the remote modem.  This
applies to both Originate and Answer Modes.  See the discussion
under Data Rate Commands, in Chapter 4.

Error Control

Always set the Courier HST for error control, &M4 (the default)
or &M5, for 9600 bps connections.

It's a good idea to find out if the remote modem is MNP-
compatible at 2400/1200 bps.  Some public network services, for
example, are not.  If the Courier HST is set to &M4 and dials a
modem that isn't under error control, it operates in Normal Mode
(no error control).  However, if the remote modem doesn't support
the MNP protocol at 2400 or 1200 bps, the MNP link-request
signals may be misinterpreted and block a successful connection.

If you know the remote modem doesn't support MNP, we recommend
setting the Courier HST to &M0 before dialing.

Automatic Retrain

An HST or V.22bis modem sends a retrain signal if it senses that
a problem in the phone line connection may be causing data
unreliability.  The modems stop the transfer of data for about a
second while they resynchronize, and then resume Data Mode
operation.

Retraining only occurs during 9600 and 2400 bps communications.
For a description of the signaling sequence, see Appendix E-3.

PLACING CALLS

The commands discussed in this section are used in the following
operations:

Dialing  D (0-9 # * , ; ! P T W @ R), DSn
RedialingA/, A>, >
Canceling dialing   <any key>

Dial (D)

When the Dial command is issued the modem goes off hook -- the
equivalent of your picking up the phone -- then enters Originate
Mode and dials the number sequence that follows.  The modem also
executes any other commands or options included in the command
line.

The command string may include up to 40 characters, plus the AT
prefix and Carriage Return/Enter key.  The modem doesn't count
spaces.  It counts punctuation characters such as parentheses and
hyphens, but ignores them.

The following command instructs the modem to stop the display of
commands (E0, turn off the local echo), to dial (D) using Touch-
Tone dialing (T), and to turn off the speaker (M0).  The spaces
shown are ignored by the modem and are only included here for
readability.

 AT E0 DT 1234567 M0 <Enter>

Dialing Type (P, T)

If set to X0 or X1, the modem defaults to pulse (rotary) dialing.
To have the modem use tone dialing, use the T command, which also
allows you to use the asterisk (*) and pound sign (#).   The
command may be included in the Dial string, as in the above
example, or issued separately:

 ATT <Enter>

The following command resets the modem to pulse dialing:

 ATP <Enter>

You can switch from one dial type to another within a dialing
sequence.  For example, you might have a phone line that only
accepts pulse dialing (slower than Touch-Tone dialing) but
subscribe to a long-distance service that accepts tone dialing,
such as  MCI.  You can switch to tone dialing once you've hooked
into the long-distance service.  In the following example, a
switch is made to tone dialing before entering a service account
number and the long-distance destination. (The commas are
discussed shortly.)

 ATDP 9,,7654321,,T 55555,,1 312 1234567 <Enter>

NOTE:  The modem remains set for Touch-Tone dialing until it is
reset or the ATP (pulse) command is reissued.

Adaptive Dialing (X2-X7)

When any of the X2 through X7 options is in effect and you don't
issue a dialing type in the Dial string, the Courier uses tone
dialing, which is faster than the default pulse type.  However,
if the phone company central office doesn't have Touch-Tone
detection equipment, the modem can not "break dial" and continues
to detect the dial tone.  If this occurs, the modem automatically
reverts to pulse dialing.

Pause (,)

A comma causes a two-second delay in the dial sequence.  The
following example contains four-second delays at several points:

 ATDP 9,,7654321,,T 55555,,1 312 1234567 <Enter>

The first four-second pause is to access an outside line after
dialing 9, the second to make sure the remote computer is ready
for the user's account number, and the third, to delay before
dialing the long-distance number.

Such pauses, however, may not be necessary.  Experiment and use
delays only as required.

NOTE:  A slash (/) can be used in any command string to have the
modem pause for only 125 milliseconds.  Some users find the
shorter delay of a series of slashes, rather than the 2-second
comma pause, useful for certain applications.

Dial and Return to Command Mode (;)

If your phone is plugged into the modem, you can use this option
to have the modem Auto Dial a telephone rather than a modem.  The
Courier dials, remains off hook and returns the OK message,
indicating it is in Command Mode.

For example, to have the modem place a voice call, issue the Dial
command with a semicolon:

 ATDT5551234; <Enter>

When the modem returns the OK result, pick up your phone receiver
so you can talk to the other party and tell the modem to hang up:

 ATH <Enter>

Similarly, you can call a recorded weather or other service.
Have the modem Dial, listen to the recording over the modem's
speaker and, when you're finished, tell the modem to hang up.

Dialing Letters (")

Quotation marks are used to have the modem dial abbreviations and
acronyms used as phone "numbers," such as DIAL USR (the
USRobotics Sales Department's 800 number).  The option is called
Quote Mode.  Quotation marks are inserted at the beginning of the
alphabetic string:

 ATDT"BBS-NEWS <Enter>

If you're including another command after the dial string, use
closing quotation marks before the additional command.

Transferring Calls (!)

This command applies to modems in installations where other
modems share the phone line.  The modem flashes the switch-hook,
i.e., goes off hook 0.5 seconds, on hook for 0.5 seconds, and off
hook again to dial the specified extension. The following example
includes instructions to return to Command Mode (;) and to hang
up (H).

 ATDT !1234;H <Enter>

Wait for a Second Dial Tone (W)

This command is useful in situations where you must wait for a
second dial tone before entering a password, for example, when
using MCI, Sprint, or other long-distance service.  The following
command tells the modem to dial the service number, wait for the
second dial tone, dial the ID, pause two seconds, then place the
long-distance call.

 ATDT 5551234 W 12345, 3121234567 <Enter>

NOTE:  This command executes only if result code option X3 or
greater has been issued.  If the modem is set to X2 or lower, the
modem interprets the W as a comma (two-second pause).

Wait for an Answer (@)

Some online services answer the phone and return a tape-recorded
request for information before processing transactions.  In such
instances, the @ command can be used in the Dial string to tell
the modem to detect at least one ring, wait for five seconds of
silence at the other end of the call, and then continue to
execute the Dial string.

To use the @ command, set the modem to X3, X4 or X7.  If the
modem is set to X2 or lower, the modem returns an ERROR message
when encountering the @ character in a command string.  If set to
X5 or X6, the modem hangs up when it detects a voice answer and
sends the VOICE result code.

In the next example, the modem is set to the X4 result code
option and dials a banking service.  Each occurrence of @ in the
example indicates a five-second wait for silence after taped
requests from the bank for the labeled items.  The transaction
code might be used, for example, to request an account balance.

Password
  |
 ATX4 DT1234567 @ 12345 @ 6789 @ 2;
   ||
  Account #  Transaction Code

If the necessary conditions don't occur -- no rings, or no
following five seconds of silence -- the modem times out as it
normally would (after 30 seconds).  It then sends the message NO
ANSWER to the screen and aborts the command.

Reversing Originate/Answer Frequencies (R)

This command allows calls to an originate-only modem.  It
reverses the modem's originate/answer frequencies, forcing the
Courier to dial out at the answer frequency.  The command follows
the Dial command, before or after the phone number:

 AT D1234567R <Enter>
 AT DR1234567 <Enter>

CANCELING DIALING

To cancel dial-command execution, press <any key>.  If you
inadvertently hit a key on the keyboard while the modem is
dialing, the call is canceled.  If this occurs, type the A/
command explained in the next section.

REDIALING

The most frequent reason for redialing is receipt of a busy
signal.  The Courier HST provides three ways to redial, as
follows.

Re-execute the Last Command (A/)

The A/ command, which doesn't take the AT prefix or a Carriage
Return, redials one time:

 A/

When the modem receives a command, it stores the instruction in
its command buffer until the next AT command is received.  Note
that if you've sent the modem an additional command since the
Dial command, A/ re-executes that command instead of redialing.

Automated Redialing (>, A>)

These two commands, while they can be used to continuously repeat
any command, are designed for automated redialing.  The first (>)
is included in the Dial command.  The second (A>) is used alone
to redial the command string in the buffer.

Continuous Repeat (>)

If you know the modem you're calling is frequently busy, include
the Repeat command in the Dial string, as follows:

 AT > DT 1234567 <Enter>
 AT DT 1234567 > <Enter>

The modem enters Repeat Mode, dials the number, waits the default
30 seconds for a carrier, and hangs up.  Then, after a two-second
pause, it redials.

The cycle continues until the modems connect or the modem reaches
a maximum of 10 attempts.  The 10-try limit is mandated by the
Canadian Department of Communications (DOC) to prevent tying up
local telephone company exchanges with unconnected calls.

Continuous Re-execute (A>)

This command combines the features of both the A/ and > commands.
The modem enters Repeat Mode as described above, and redials the
Dial string in the command buffer.  Like the A/ command, A>
doesn't take the AT prefix or a Carriage Return:

 A>

Exiting Repeat Mode

Should you use > or A> with a command other than a Dial string,
abort the cycle by pressing <any key>.

To abort automated redialing, be sure to press <any key> when the
result code appears, during the pause before the modem begins
dialing again.  If you press <any key> while the modem is
dialing, that dial attempt is canceled but the cycle continues.

DIALING A STORED NUMBER (DSn)

Chapter 5 includes instructions for storing up to four telephone
numbers in nonvolatile random access memeory (NRAM).  To have the
modem dial a stored number use the DSn command, where n is the
number's position, 0-3, in NRAM.  In the first of the next two
examples, the phone number is stored at position 0, assumed by
the modem if there is no numeric parameter:

 ATDS <Enter>
 ATDS3 <Enter>

If you've stored a long distance service number/access code, for
example at position 1, use the DSn command to dial the number and
code, and follow that with a Dial command to dial the call's
destination.  (The spaces are included for readability.)

 AT DS1 D 312 5556789 <Enter>

ESCAPE CODE OPERATIONS (+++)

Once the modem is online to another system, the only command it
recognizes is an escape code of three pluses, which forces the
modem back to Command Mode:

-- Wait one second after entering the last item of data

-- Type: +++

-- Wait one second before typing any data

Do not type the AT prefix or a Carriage Return.  The guard time
of one second before and after the code prevents the modem from
misinterpreting the occurrence of +++ in the transmitted data
stream.

If necessary, the character used in the escape code or the
duration of the guard time can be changed by resetting S-register
2 or 12.  See Appendix B-5.

Modem Response to +++

The modem returns to Command Mode when it detects the escape
code.  However, it keeps the line open or hangs up, depending on
the setting of DIP switch 9:

DIP Switch 9   Response to +++
UP Modem goes on hook (hangs up), sends NO
CARRIER result code
   DOWNModem maintains connection, sends OK result
code (Factory Setting)

Retain the factory-set position (DIP switch 9 DOWN) if you want
the modem to execute commands and return online.  (See the O
command, below.)

If you want an automatic disconnect when you issue +++, set
switch 9 UP.  (If the modem is on, also issue the ATZ command.)
An advantage of this is that you're not likely to inadvertently
run up an all-night phone bill.

WARNING

For unattended modem operations:  in rare instances, the modem
may fail to recognize the +++ escape code sequence.  If you are
running the modem under software control for unattended
operations, we suggest you use the surefire method of dropping
the RS-232C DTR signal for at least 50 milliseconds, to ensure
against costly phone charges.  Methods of turning the DTR signal
off, e.g., closing the communications port, differ from one
computer to another.

RETURNING ONLINE (O)

If DIP switch 9 is DOWN (on detection of the escape code the
modem maintains the connection), you can issue commands and then
toggle the modem back online with the O command, as in this
example:

 AT Q1 O <Enter>

HANGING UP (Hn)

If DIP switch 9 is DOWN (factory setting), the escape code forces
the modem back to Command Mode but leaves the line open.  To
instruct the modem to hang up, issue the following command once
the modem sends the OK result code:

 ATH <Enter>

If DIP switch 9 is UP, the modem automatically hangs up on
receipt of the escape code.

AUTOMATIC ANSWERING

The Courier HST is shipped with DIP switch 5 DOWN, Auto Answer
suppressed.  To set the modem to automatically answer incoming
calls, do one of the following:

1.   Before powering on the modem, set DIP switch 5 UP.  When you
turn the modem on, it answers incoming calls on the first
ring.

2.   If the modem is on, use software control.  The following
command instructs the modem to answer on the first ring.
(You can substitute a higher value.  See the S-Register
summary in Appendix B-5.)

 ATS0=1 <Enter>

When the modem senses a call coming in, it sends the result code
RING to your screen, goes off hook, and sends the remote modem a
high-pitched answer tone.  If there is no Carrier Detect within
30 seconds, the modem hangs up. If the connection is made, the
modem sends a CONNECT result code.  When the call is disconnected
by you or the remote user, the modem hangs up and returns the NO
CARRIER code.

Suppressing Auto Answer

To disable Auto Answer, reverse steps 1 or 2 above.  Set DIP
switch 5 DOWN before powering on the modem or, if it is powered
on, use the command to set the modem to answer on zero rings:

 ATS0=0 <Enter>

Points to Remember

1.   If the modem is attached to a computer, you can set the
modem to receive calls when you're not there.  Put the modem
in Terminal Mode and set it for Auto Answer.  Also set your
software's file-save function to save incoming messages
and/or files.

2.   If you've attached your phone so it can be used for
conventional calls, disable Auto Answer when you're not
expecting incoming data calls.  Otherwise, your modem may
answer the phone before you do, greeting a voice caller with
a high-pitched, irritating answer tone.

INTERNATIONAL CALLS

The Courier HST has three settings which enable international
calls.  These settings do not apply to calls originating in the
U.S. or Canada.

U.S./CCITT Answer Tone (Bn)

In the United States and Canada, modems use a 2225 Hz answer
tone.  Outside North America, most modems adhere to the CCITT
V.25 standard and send out a 2100 Hz tone followed by a 2250 Hz
tone.  If you're expecting an overseas call, set the Courier to
use the CCITT answer tone.  The setting won't affect the modem's
ability to connect with a domestic modem, although it will take
slightly longer to connect with a calling modem.

B0   CCITT answer sequence, used to answer calls calls
originating outside North America.  Required with &G2
setting.

B1   U.S. answer tone.  Default.

Guard Tone (&Gn)

British phone switching systems require the modem to send an 1800
Hz guard tone after it sends an answer tone.  The guard tone is
not used in the United States or Canada.

&G0  No guard tone, U.S./Canada.  Default.

&G1  Reserved.

&G2  1800 Hz guard tone follows answer tone, United Kingdom and
some Commonwealth countries.  Requires B0 setting as well.

Pulse Dial Make/Break Ratio (&Pn)

This command sets the ratio of the off-hook/on-hook (make/break)
interval for pulse dialing.  The default sets the modem for use
in North America.  The ratio must be changed if the modem is used
in the United Kingdom and some Commonwealth countries.

&P0  Make/break ratio, U.S./Canada:  39%/61%.  Default.

&P1  Make/break ratio, United Kingdom, some Commonwealth
countries:  33%/67%.


                 CHAPTER 7 - QUERIES AND HELP SCREENS

USER INQUIRIES (In)

The Inquiry command has eight options.  The most commonly used
options display the following information:

ATI3  Call duration
ATI4  Current settings
ATI5  NRAM settings
ATI6  HST link diagnostics summary

I0   The modem returns a 3-digit product code.  If you have a
problem and call USRobotics' Technical Support Department,
you may be asked for this product code.

I1   The modem performs a checksum of its read only memory (ROM)
and returns the result to the screen.  This function is used
only in factory testing.  The modem should always read the
same number.

I2   The modem performs a test of its random access memory (RAM)
and returns either the OK (0) or ERROR (4) result code,
followed by OK when the test is completed.  You may want to
use this command as a checkpoint if the modem appears to be
malfunctioning.

I3   The modem returns the duration of the last call if set the
K0.  It displays the actual time if set to K1.  See the
description of the Kn command in Chapter 5.

I4   The modem displays its current configuration.  The following
illustration is an example.


Figure 7.1 -- Sample Result of ATI4 Command


I5   The modem displays the configuration stored in nonvolatile
random access memory (NRAM).


Figure 7.2 -- Sample NRAM Settings Screen


I6   During a connection, the modem monitors and stores
information about link operations.  When the call is ended,
you can request a diagnostic summary, as in the following
example.


  Figure 7.3 -- Sample Link Diagnostics Screen (ATI6)


Terms used in the display are self-explanatory except for
the following:

Octets   Compressed characters
BlersErrors in protocol (non-data) blocks
Link NaksNegative acknowledgments (one or more
  blocks)
Link Timeouts   Protocol operations, not the retry
  timeout; used in internal testing
Data CompressionOn/Off: indicates if data compression
  was negotiated for the call
EqualizationLong/Short: status of S15 bit 0; long if
  bit 0=0, short if bit 0=1
Fallback Enabled/Disabled: indicates whether or
  not the modems negotiated online
  fallback during the connection sequence

I7   The modem returns a product configuration.  If you have a
problem and call USRobotics' Technical Support, you may be
asked to read this screen.

S-REGISTER QUERY (Sr?)

This command allows you to view the contents of a particular S-
Register, as in the following example that requests the contents
of register S0 ("On what ring will the modem answer?"):

 ATS0? <Enter>

Most registers store values that can be user-defined.  However,
two registers that are not user-programmable can be queried for
the following diagnostic information.

S17  The reason for a Link Disconnect when two modems try to make
an ARQ connection and fail, or when the remote modem
disconnects from an ARQ session.  S17 is used for debugging
purposes.  If you're having an ARQ-compatibility problem and
call USRobotics' Technical Support, you may be asked to
check S17.

S20  The reason for a NO CARRIER result code when the modem is in
either ARQ or Normal Mode.  Reasons include user aborts
(pressing <any key> during dialing), loss of carrier, and
the automatic hangup that occurs when the modem is set to
&M5 and calls a modem not operating under error control.


PHONE NUMBER QUERY (&Zn?)

At this command, the modem returns the phone number stored in
NRAM at position n, as in the following example that includes a
sample modem response:

 AT&Z3? <Enter>
 5551234

HELP SCREENS

The Courier HST provides four Help screens:  summaries of the
basic AT command set, extended ampersand (&) command set, S-
register functions, and Dial command options.

Stop/Restart Display

The following command stops the display. Hold down the Control
key and type "S":

 <Ctrl>-S

To restart the display, use the same command or press <any key>.

Cancel Display

Either of the following commands cancels the display.

 <Ctrl>-C
 <Ctrl>-K

Basic Command Set ($)

At AT$, the Courier displays this command set summary:

Figure 7.4 -- Basic Commands HELP Screen


Extended Command Set (&$)

At AT&$, the Courier displays this summary of the ampersand
command set:


 Figure 7.5 -- Ampersand Commands HELP Screen


S-Register Functions (S$)

At ATS$, the Courier displays a summary of the S-register
functions:


  Figure 7.6 -- S-Register HELP Screen


Dialing (D$)

At ATD$, the Courier displays this Dial command summary:


 Figure 7.7 -- Dial Command HELP Screen


            APPENDIX A - ERROR/FLOW CONTROL CONCEPTS

At 2400 and 1200 bps, the Courier HST uses the MNP error control
protocol, Service Levels 1-5.  MNP was originally developed by
Microcom, Inc. and is now in the public domain.  At 9600, 7200
and 4800 bps the modem uses similar, compatible error control
procedures developed by USRobotics.

In USRobotics implementations, we use the general term ARQ
(automatic repeat request) to denote a connection under error
control.  Error-free data transmission is ensured through two
features:

oerror-detection and retransmission techniques;

odata buffering and flow control.

NOTE:  As with all protocols, error control only works when the
Courier HST connects with another modem that implements the same
protocol.

MNP LEVEL NEGOTIATION

When the modems negotiate an ARQ connection, they indicate their
highest of the first three Service Levels, 3, 2, or 1, and agree
to operate at the highest possible level.  The Courier HST
indicates Level 3 in its MNP error-control parameter.  If
necessary, the Courier drops back to meet the requirements of the
other modem.  This establishes the error-control (ARQ)
connection.

Levels 4 and 5, which enhance throughput performance, are only
possible if an ARQ connection is established.  The Courier
negotiates for a Level 4 connection, with the longer, streamlined
transmission frames described below.  Whether or not Level 4 is
agreed upon, the Courier also negotiates for a Level 5 connection
(data compression).  It's possible for an ARQ connection to be at
Level 1, 2 or 3, with or without Level 4 and/or Level 5.

Throughput

Chapters 3 and 4 include recommended modem settings and file-
transfer guidelines for gaining maximum throughput.  The
following descriptions of MNP Levels 1-5 include achievable
throughput statistics.

Level 1

This level, often called Block Mode, supports half-duplex (one
way at a time) transmission.  The sending modem transmits a block
of data and waits for an acknowledgment from the receiving modem
before sending the next.

Level 1 is the slowest and is included because some computer
equipment is restricted to either sending or receiving at any one
time.  This mode of operation is usually observed in
communications between terminals rather than in terminal-to-
computer or computer-to-computer links.

Level 2

This level, often called Stream Mode, supports full-duplex
transmission in which data flows in both directions at the same
time.  Throughput at Level 2, due to protocol overhead, achieves
about 84% of the throughput of a normal modem, or approximately
202 characters per second (cps) at 2400 bps.

Level 3

Level 3 incorporates Level 2 and is more efficient.  Modems
sending at Level 3 strip the Start and Stop bits from the data
characters and transmit the data across the link in bit format,
as in synchronous transmission, rather than in character format.
The receiving modem reinserts the Start and Stop bits for each
character before passing the data to the receiving computer or
terminal.

This procedure offsets the protocol overhead loss so that
throughput is about 108% that of a normal modem.  Under optimal
conditions, two Level 3 modems operating at 2400 bps can exchange
data at approximately 254 characters per second.

Level 4

At this level, the information in the headers of transmission
frames is streamlined to eliminate some of the protocol overhead.
In addition, the size of the frames is greater than with Level 3.

The results in characters per second (cps) are as follows.  These
reflect operations without the data compression available with
MNP Level 5.

Characters per Second
Link Rate  Level 3   Level 4
96001100  1160
2400 254   276

In general, with Level 4 you can expect a throughput gain of 5%,
although actual throughput depends on the type of call.  Gains on
long-link satellite calls can range from 25-50%.

Level 5

Under data compression, the sending modem detects redundant units
of data and recodes them into shorter units of fewer bits.
Examples include the frequent occurrences of spaces, control
characers, or the characters e and s in ASCII text files.  The
receiving modem decompresses the redundant data units before
passing them to the receiving computer/terminal.

With data compression, throughput of up to 19.2k bps is possible.
Achievable throughput rates for different kinds of files, in
characters per second (cps), are shown in the following table.

The table assumes the following optimal conditions:

oDTE rate set at 19.2k bps; modem set to &B1
oConnection (link) rate of 9600 bps
oLevel 4 also enabled (longer transmission frames)
oStraight data (e.g., not already compressed, no file-
 transfer protocol)
oTransmission from a fast (e.g., 286) computer

File TypeThroughput (cps)
Assembler or Compiler Listing  1920
Text file 1550-1750
Binary file:  .EXE  1450-1600
Binary file:  .COM  1400-1500
.ARC files (common on BBS's)   1000-1100*
Random binary 8-bit  975-1050*

*As mentioned on Page 4-2, these files are already
compressed or appear to the modem to be compressed.  If they
undergo additional data compression, they become longer.

ERROR DETECTION/RETRANSMISSION

During an ARQ connection the transmitting modem divides the data
it receives from the computer or terminal into blocks, and
attaches header and trailer information.  The result is called a
frame, as shown in Figure A.1.


Figure A.1 -- Transmission Frame


Included in the header or trailer are a frame number and block-
size information as well as a frame-check code.  This last code
is derived by the sending modem through an algorithm performed on
all of the data in the frame.  The technique is called cyclic-
redundancy checking (CRC).

The receiving modem performs the same computation and checks to
see if its results match the received CRC code.  If the results
match, the receiving modem sends a positive acknowledgement to
the sending modem.  Meanwhile, the sending modem keeps a copy of
all frames it sends until each is positively acknowledged.

If the CRC codes don't match, the receiving modem initiates the
automatic repeat request (ARQ) procedure.  The receiving modem
tells the sending modem which frame is in error, and doesn't
accept any more frames until the frame in question is received
correctly.  The sending modem goes back to the specified frame,
retransmits it, and continues from there.  In this way the
protocol protects against errors and also ensures that the data
arrives in sequence.

FLOW CONTROL

The modem stores data from the DTE in its Transmit buffer, and
data received from a remote system in its Receive buffer, as
shown in Figure A.2.


Figure A.2 -- Flow Control Buffer


Separate commands enable Transmit Data flow control (&Hn) and
Received Data flow control (&In, &Rn).  Chapter 4 contains
instructions on when and how to use these commands.

Flow Control Examples

The labels used in the following examples indicate the following
devices:

DTE  Data Terminal Equipment:  the computer or terminal to which
a modem is attached.

DCE  Data Communications Equipment:  the Courier or remote modem.

Example 1 -- Transmit Data

The &Hn command allows you to select software flow control,
hardware flow control, or both.  Hardware flow control is most
reliable and is recommended, if possible.  Under hardware control
the modem raises or lowers the Clear to Send (CTS) signal via the
RS-232C interface.  Under software flow control the modem sends
the DTE the ASCII XON/XOFF characters described in Chapter 4.


   Figure A.3 -- Transmit Flow Control


Assume that there are disturbances on the line (line hits) and
DCE2, the receiving modem, detects a transmitted frame error.
DCE2 tells DCE1 to retransmit the frame and accepts no additional
frames until it receives the affected frame correctly.

Meanwhile, the computer/terminal (DTE1) continues sending to
DCE1, and data backs up in the Transmit buffer.  As the buffer
approaches capacity, DCE1 signals DTE1 to stop sending data.
DCE1 also retransmits the specified frame and continues
transmitting.  When enough data is transmitted to half empty the
buffer, DCE1 signals DTE1 to resume sending data.

As mentioned in Chapter 4, Transmit Data flow control is also
essential if the DTE is set to send to the modem at a rate higher
than the link rate.

Example 2 -- Received Data

It may be necessary or desirable to stop incoming data
temporarily, for example, in order to review what's on the screen
and take some kind of action.  In the following diagram, the
labels indicate operations when three different command options
are used, as follows:

&I1  The user at DTE1 sends an XOFF command to the modem to
 have it stop passing on data from the Receive buffer.
 The modem also transmits the XOFF to the remote
 computer, which stops sending.  DCE1 resumes passing
 received data to DTE1 when the user sends an XON
 signal.

&I2  The user sends the same XON/XOFF commands to DCE1, but
 the modem doesn't pass them on to the remote computer.

&R2  DTE1 lowers the Request to Send (RTS) signal at the RS-
 232C interface.  This signals DCE1 to stop passing on
 received data.


Figure A.5 -- Received Data Flow Control


Be sure to review Chapters 3 and 4 before using the error/flow
control commands.


              APPENDIX B - SUMMARIES AND TABLES

CONTENTS

B-1  The RS-232C Interface, with Pin Definitions

B-2  Front End Indicators

B-3  DIP Switch Summary

B-4  Default Settings

B-5  S-Register Summary

B-6  ASCII Chart


       APPENDIX B-1 - THE RS-232C INTERFACE, WITH PIN DEFINITIONS

DESCRIPTION

The RS-232C interface (often referred to without the C) is a
standard developed by the Electronic Industries Association
(EIA).  It defines the signals and voltages used when data is
exchanged between a computer or terminal and a modem or serial
printer.  Data is transmitted between the devices via a cable
with 25-pin, 9-pin or custom-built connectors.

PIN ASSIGNMENTS

The entire standard covers many more functions than are used in
most data communications applications.  Pin assignments are
factory set in the Courier 2400e to match the standard DB-25
assignments in the following table.  DB-9 connectors at the
computer/terminal end of the cable should be wired to reflect the
pin assingments in the DB-9 column.

   RS-232C INTERFACE PIN DEFINITIONS

  DB-25   DB-9 CircuitFunction Signal Flow
2  3  BA  Transmitted DataTerminal  ®  Modem
3  2  BB  Received Data   Terminal  ¬  Modem
4  7  CA  Request to Send Terminal  ®  Modem
5  8  CB  Clear to Send   Terminal  ¬  Modem

6  6  CC  Data Set Ready  Terminal  ¬  Modem
7  5  AB  Signal Ground   Terminal  «  Modem
8  1  CF  Carrier Detect  Terminal  ¬  Modem
12 --SCF  Speed Indicate  Terminal  ¬  Modem

20 4  CD  Data Terminal Ready Terminal  ®  Modem
22 9  CE  Ring Indicate   Terminal  ¬  Modem

MINIMUM REQUIREMENTS

Some computer/terminal equipment supports only a few of the RS-
232C signal functions set in the Courier.  The minimum required
for the modem to operate are as follows:

  DB-25   DB-9
   PinPin  Function
2  3   Transmitted Data
3  2   Received Data
7  5   Signal Ground
20 4   Data Terminal Ready*

* Required only if you have set the Data Terminal Ready (DTR)
Override switch (DIP switch 1) OFF (UP).

If your computer and software support Clear to Send and you wish
to use Transmit Data hardware flow control (&H1), Pin 5 (DB-25)
or Pin 8 (DB-9) is required.  If your computer and software
support Request to Send and you wish to use Received Data
hardware flow control (&R2), Pin 4 (DB-25) or Pin 7 (DB-9) is
required.


             APPENDIX B-2 - FRONT END INDICATORS

SymbolMeaningStatus

 HS  High Speed 9600-bps calls only:  ON during call
  progress, after completion of dialing;
  OFF during link negotiations at 2400
  bps; ON during connection.  Remains ON
  after disconnect until next call is
  originated or answered.

   AAAuto Answer/   Answer Mode only:  ON when
 your modem is  Answer   in Auto Answer Mode,
 and when answeringa call; goes
 OFF if the channel isrever
 sed and your modem transmits at
 450 bps.  Also goes off when the modem
   originates a call.

 CD Carrier Detect  ON when the CD override (DIP switch 6)
  is ON (DOWN).  ON if DIP switch 6 is UP
  and the Courier receives a valid data
  signal (carrier) from a remote modem,
  indicating that data transmission is
  possible.

 OH  Off Hook   ON when the Courier takes control of the
  phone line to establish a data link.

 RD  Received Data  Flashes when a data bit is received by
  the Courier from the phone line, or when
  the modem is sending result codes to the
  terminal or computer.

 SD  Send Data  Flashes when a data bit is sent to the
  Courier by the terminal or computer.

 TR  Terminal Ready ON when the DTR override (DIP switch 1)
  is ON (DOWN).  ON if DIP switch 1 is UP
  and the modem receives a Data Terminal
  Ready signal from the terminal or
  computer via the RS-232C interface.

   MRModem Ready/   ON when the Courier is powered
 on. PowerFlashes when the
 modems retrain,  inclu
 ding online fallback to 7200 or
 4800 bps.

 RS  Request to ON when the Courier is powered on if
 Sendyour computer supports RTS on the RS-
  232C interface.  OFF if the Courier is
  set to &R2 (Received Data hardware flow
  control) and the computer lowers RTS.

 CS  Clear to Send  ON until the modem lowers CTS on the RS-
  232C interface when Transmit Data
  hardware flow control is enabled (&H1,
  &H3).

 ARQ Error Control  Automatic Repeat Request.  ON when the
  Courier is set to &M4 or &M5 and
  successfully connects with another modem
  under error control.

 AL  Analog ON when the modem is in Analog Loopback
   Loopback   Self-Test Mode.


               APPENDIX B-3 - DIP SWITCH SUMMARY

PURPOSE

The Courier's DIP switches, located at the rear of the modem, are
for adapting the modem to your equipment and personal
requirements.  You may also want to experiment and review your
computer or terminal documentation as necessary.

Some users are able to move a single switch with a finger tip.
If this doesn't work for you, use a toothpick or other small
instrument.

OPERATIONS

The DIP switch settings are power-on defaults, read by the
Courier when it is turned on.  If changed when the modem is on,
switches 2-5 and 9 require the ATZ (software reset) command to
initiate the new settings.  The remaining (hardware) switches are
automatically operative when set UP or DOWN.


  DIP SWITCHES:  UP = OFF (OPEN), DOWN = ON (CLOSED)

 Factory
SwitchSetting   Function

 1   DOWN  Data Terminal Ready (DTR) Operations
UP   Normal DTR operations; computer must
  provide DTR signal for modem to accept
  commands; dropping DTR terminates a call
DOWN DTR always ON (Override)

 2   UPVerbal/Numeric Result Codes
UP   Verbal (word) messages
DOWN Numeric codes

 3   DOWN  Result Code Display
UP   Quiet Mode, no display
DOWN Result codes displayed

 4   UPCommand Mode Local Echo
UP   Keyboard commands displayed
DOWN Display of commands suppressed

 5   DOWN  Auto Answer
UP   Modem answers on first ring
DOWN Auto Answer suppressed

 6   DOWN  Carrier Detect (CD) Operations
UP   Courier sends CD signal when it connects
  with another modem, drops CD on
  disconnect
DOWN CD always ON (Override)

 7   UPSingle/Multiple Phone Installation
UP   Single phone line connection (RJ11 jack)
DOWN Multiple phone installations (RJ12 or
  RJ13 jack); shorts A/A1 to notify other
  devices when modem goes off hook and
  line is busy

 8   DOWN  Command Set Recognition
UP   Rrecognition disabled (Dumb Mode)
DOWN Recognition enabled (Smart Mode)

 9   DOWN  Escape Code (+++) Response
UP   Modem hangs up, returns to Command Mode,
  sends NO CARRIER result
DOWN Modem maintains connection, returns to
  Command Mode, sends OK result

10   UPPower-on and ATZ Reset Software Defaults
UP   Load from NRAM
DOWN Load factory settings from ROM

Quad UPRS-232C Transmitted/Received Data Pin
SwitchAssignments
UP   Normal assignments: see Appendix B-1
DOWN Reverse assignments

The need to change this setting is rare.
Carefully review your computer or terminal
documentation before turning this switch ON.


                 APPENDIX B-4 - DEFAULT SETTINGS

USER-PROGRAMMABLE DEFAULTS

You can create your own default configuration and store it in
nonvolatile random access memory (NRAM) using the &W command
described in Chapter 5.  Your defaults are then loaded into
random access memory (RAM) as long as DIP switch 10 is UP when
you power on the modem.  To view your NRAM settings at any time,
use the ATI5 command.

The following table lists the options stored in NRAM.  If DIP
switch 10 is DOWN at power on, the factory settings listed in the
table are loaded instead.  The first time the modem is turned on,
the NRAM settings are the same as the factory settings.


NRAM Options  Factory Setting

Normal/error control modes &M4  Normal/ARQ
Data compression&K1  Auto enable/disable
Error-control result codes &A1  Enabled
Transmit data flow control &H0  Disabled
Received data software flow control&I0  Disabled
Received data hardware flow control&R1  Ignore RTS

DTE rate select &B0  Follow connection rate
Link rate select&N0  Variable link operations
Data Set Ready (DSR) signal&S0  Override

Stored telephone number &Z0-3=0   Blank
Tone/Pulse dialing  PPulse dial
Online local echo   F1   Echo OFF
Speaker control M1   ON during dial through connect
Result code setsX1   Extended

Pulse dial make/break ratio&P0  N. American
U.S./CCITT answer tone  B1   N. American
Guard tone   &G0
Break handling&Y1  Clear buffer, send Break
  immediately
Word length  7*
Parity   1*   Even parity

*Detected from AT command; determined by terminal/software
setting.


NRAM S-Register Option   Factory Setting

Escape code character, ASCII decimal S2=43
Carriage Return character, ASCII decimal S3=13
Line Feed character, ASCII decimalS4=10
Backspace character, ASCII decimal S5=8
Dial wait-time, sec.S6=2

Carrier wait-time, sec.S7=30
Dial pause/re-execute time, sec.   S8=2
Carrier Detect time, 1/10th sec.   S9=6
Carrier loss wait-time, 1/10th sec.S10=7
Touch-Tone duration, spacing, msec. S11=70

Escape code guard time, 1/50th sec. S12=50
Bit-mapped functions, S-Register 13S13=0
Bit-mapped functions, S-Register 15S15=0
Inactivity/hang up timer, S-register 19  S19=0

Received break length, 10-msec. units   S21=10

XON character, ASCII decimal S22=17
XOFF character, ASCII decimalS23=19


               APPENDIX B-5 - S-REGISTER SUMMARY

USAGE

The default values are those users typically require.  Change the
settings with the ATSr=n command, where r is the register and n
is a decimal value from 0-255:

 ATS13=8 <Enter>

The modem does not perform a value-range check.  Some values may
not work with some equipment, and you'll have to readjust the
settings.

To display the contents of a register, use ATSr? as in this
example:

 ATS20? <Enter>


Register  Default   Function

 S0 See DIPSets the number of rings on which to answer
 Switch 5   when in Auto
Answer Mode.  Default = 1, equivalent of DIP switch 5 UP.  S0=0
or DIP switch 5 DOWN (factory setting) suppresses Auto Answer.

 S1 0   Counts and
stores the number of rings from an incoming call.

 S243  Stores the ASCII decimal code for the escape
code character.  Default character is "+".  A value of 128-255
disables the escape code.

 S313  Stores the ASCII decimal code for the
Carriage Return character.

 S410  Stores the ASCII decimal code for the Line
Feed character.

 S5 8  Stores the ASCII decimal code for the
Backspace character.  A value of 128-255 disables the Backspace
key's delete function.

 S6 2  Sets the number of seconds the modem waits
before dialing.  If set to X2, X4, X6, or X7, the modem ignores
this register and dials as soon as it detects a dial tone (fast
dials).

 S730Sets the number of seconds the modem waits  for a
carrier.  May be set for much longer  duration if, for example,
the modem is  originating an international connection.

 S8 2  Sets the duration, in seconds, for the pause
(,) option in the Dial command and the pause between command re-
executions (> and A> commands).

 S9 6  Sets the required duration, in tenths of a
second, of the remote modem's carrier signal before recognition
by the Courier (Carrier Detect Time).

 S107  Sets the duration, in tenths of a second,
that the modem waits after loss of carrier  before hanging up.

 S11   70Sets the duration and spacing, in milliseconds, of
dialed Touch-Tones.

 S12   50Sets the duration, in fiftieths of a second, of the
guard time for the escape code sequence.

 S130   Bit-mapped
register.  Select the bit(s) you want on, and set S13 to the
total of the values in the Value column.  For example, ATS13=20
enables bits 2 (value = 4) and 4 (value = 16).

Bit  Value  Result
 0 1Reset on dropping of DTR
 1 2Reverse normal Auto Answer
 operation:  on incoming RING,
 enter Originate Mode and look for
 Answer tone
 2 4Disable 250 msec. pause before
 result code display
 3 8On DTR signal, Auto Dial number
 stored in NRAM at position 0
 4 16   At power on/reset, Auto Dial
 number stored in NRAM at position
 0
 5 32   Reserved
 6 64   Disable MNP Level 3 (used for
 testing Level 2)
 7128   Watchdog hardware reset, same as
 power on (used in factory
 testing)

 S14 Reserved.

S15 0   Bit-mapped
register.  See instructions for S13, above.

Bit  Value  Result
 0   1      Disable the modem's extra high-frequency equalization if it
            causes problems on shorter-link calls
 1   2      Disable 7200/4800 bps online fallback
 2   4      Disable 450-bps back channel, force 300-bps back channel
 3   8      Reset non-ARQ mode Transmit buffer from 1.5k bytes to 128 bytes*
 4  16      Disable MNP Level 4; retransmitting the larger Level 4 data blocks
            may be a problem if you expect a great number of errors during a
            call
 5  32      Set Del key to act as Backspace key; provided for specialized
            applications.  May cause software incompatibility in standard
            applications.
 6  64      Some earlier 2400-bps MNP modems, not made by USRobotics or
            Microcom, were not fully compatible with the MNP protocol.  If you
            have difficulty making a successful 2400-bps MNP connection with a
            remote MNP modem, it may be because of this incompatibility.  Set
            S15 to 64 and try again to make the connection.
 7  128     Enable Interbridge network compatibility

* The default 1.5k byte non-ARQ buffer allows
data transfer with X- and YMODEM-type file
transfer protocols without using error
control.

The 128-byte option allows remote users with
slower modems to stop data you're
transmitting from scrolling off their
screens.  When remote users send your
computer an XOFF (Ctrl-S) and you stop
transmitting, the data in transit from your
modem's buffer doesn't exceed the size of
their screen.

S160 Modem self-
test.  See Appendix E-6 for test procedures.

0  Data Mode (no testing)
1  Analog Loopback
2  Dial Test
4  Test Pattern
5  Analog Loopback with Test Pattern

 S170   Stores the
reason for a received ARQ Link Disconnect. May be requested by
Technical Support if you're having a problem connecting in ARQ
mode with another ARQ-mode modem. At ATS17?, the modem returns
one of the following codes.

 1   Received data unit other than link request
 2   Incompatible protocol level (3, 2, 1)
 3   Unknown parameters in link request
 4   Remote modem retry timeout (Max. 12 tries)
 5   Inactivity timeout (See S19)
 6   Destination user not found
254  Peer protocol error
255  User-initiated disconnect

 S18 Reserved.

 S190   Sets the
duration, in minutes, for the Inactivity Timer.  The timer is
activated when there is no activity on the phone line.  At the
timeout the Courier hangs up.

S20 0   Stores the
reason for the NO CARRIER result code.  At ATS20? the modem
returns one of the following codes:

 0   Key press abort
 1   DTR dropped
 2   Escape code (+++) issued
 3   Loss of Carrier
 4   Inactivity timeout
 5   Automatic hangup with ARQ incompatibility (&M5 Mode)
 6   ARQ Retry timeout (Max. 12 tries)
 7   ARQ Received Link Disconnect (See S17)

 S21   10   Sets, in 10-
millisecond units, the length of Breaks sent from the modem to
the local terminal.

 S22   17   Stores the
ASCII decimal code for the XON character.

 S23   19   Stores the
ASCII decimal code for the XOFF character.


APPENDIX B-6 - ASCII CHART


              APPENDIX C - ALPHABETICAL COMMAND SUMMARY

Additional command summaries are on the bottom panel of the modem
and in the Quick-Reference Card.

Requirements

1.   Type commands in either upper or lower case.

2.   All commands except A/, A> and +++ are preceded by the AT
prefix and are executed with the Enter/Carriage Return key
(<Enter>).

3.   Command length = 40 characters maximum.  The modem doesn't
count the AT prefix, Carriage Return character, or spaces.
It counts but doesn't act on punctuation such as hyphens and
parentheses.

4.   A missing numeric parameter is assumed to be zero, as in the
command to hang up:  ATH <Enter> is the equivalent of ATH0
<Enter>.

 BASIC COMMAND SET


Command/Options Function

&See the Extended Command Summary that follows this Basic
Set.

AForce Answer Mode when the modem hasn't received an incoming
call.

A/   Re-execute the last issued command one time.  A/ doesn't
take the AT prefix or a Carriage Return.

A>   Re-execute the last issued command continuously until
canceled by pressing <any key>.  Dial strings are re-
executed ten times after which execution terminates.  A>
doesn't take the AT prefix or a Carriage Return.

<Any key> Terminate current dialing operation resulting from an
issued Dial command; terminate Repeat mode (> or A>).

AT   Attention:  lets the modem know commands are being issued to
it.  Must precede all other commands except A/, A> and +++.

Bn   U.S./CCITT answer sequence.

B0   U.S. answer sequence (Default).

B1   CCITT (overseas) answer sequence.

Cn   Transmitter enabled/disabled.

C0   Transmitter disabled; receive-only condition.

C1   Transmitter enabled (Default).

DDial the number that follows and enter Originate Mode.
Optional parameters:

PPulse dial (Default).
TTouch-Tone dial.
,(Comma) Pause for 2 seconds.
;Return to Command Mode after dialing.
"Dial the letters that follow.
!Transfer call (flash switch-hook).
WWait for second dial tone (with X3 or higher).
@Wait for an answer (with X3 or higher).
RReverse frequencies.

DSn  Dial the phone number stored in NRAM at position n (n = 0-3).

En   Command Mode local echo (display) of keyboard commands ON/OFF.  (DIP
     switch 4 is factory set to Command Mode echo ON.)

E0   Local echo OFF.

E1   Local echo ON.

Fn   Online local echo of transmitted data ON/OFF.  Sometimes referred to as
     the Duplex setting.

F0   Local echo ON.  Sometimes called Half Duplex.  Modem sends a copy to your
     screen of data it sends to the remote system.

F1   Local echo OFF (Default).  Sometimes called Full Duplex.  Receiving
     system may send a remote echo of data it receives.

Hn   On/off hook control.

H0   Hang up (go on hook).

H1   Go off hook.

In   Inquiry.

I0   Display product code.

I1   Display results of ROM checksum.

I2   Display results of RAM test.

I3   Display call duration or real time (see Kn).

I4   Display current modem settings.

I5   Display NRAM settings.

I6   Display link diagnostics.

I7   Display product configuration.

Kn   Modem clock operation:  Call-duration or Real-time Mode.

K0   Return call duration at ATI3 (Default).

K1   Return actual time at ATI3.  Clock is set using ATI3=HH:MM:SS K1.

Mn   Monitor (speaker) control.

M0   Speaker always OFF.

M1   Speaker ON until carrier is established (Default).

M2   Speaker always ON.

M3   Speaker ON after last digit dialed and until carrier is established.

O    Return online after command execution.

P    Pulse dial (Default).

Qn   Quiet Mode:  result codes displayed/suppressed.  (DIP switch 3 is factory
     set to display result codes.)

Q0   Result codes displayed.

Q1   Result codes suppressed ("quiet").

Sr=n S-register commands:  r is any S-register; n must be a decimal number
     between 0 and 255.

Sr?  Query register r.

T    Tone dial.

Vn   Return result codes in words or numbers (Verbal/Numeric Mode).  (DIP
     switch 2 is factory set to verbal result codes.)

V0   Numeric Mode.

V1   Verbal Mode.

Xn   Result code set options.  Use the following table (Default=X1, Extended
     set, codes 0-5, 10).

                       RESULT CODES OPTIONS TABLE

                                              Commands
                                    X0  X1  X2  X3  X4  X5  X6  X7
       Result Codes
        0/OK                         X   X   X   X   X   X   X   X
        1/CONNECT                    X   X   X   X   X   X   X   X
        2/RING                       X   X   X   X   X   X   X   X
        3/NO CARRIER                 X   X   X   X   X   X   X   X
        4/ERROR                      X   X   X   X   X   X   X   X
        5/CONNECT 1200                   X   X   X   X   X   X   X
        6/NO DIAL TONE                       X       X       X   X
        7/BUSY                                   X   X   X   X   X
        8/NO ANSWER                              X   X   X   X   X
        9/Reserved
       10/CONNECT 2400                   X   X   X   X   X   X   X
       11/RINGING                                        X   X   X
       12/VOICE                                          X   X
       13/CONNECT 9600                   X   X   X   X   X   X   X

      Functions
       Adaptive Dialing                      X   X   X   X   X   X
       Wait for 2nd Dial Tone (W)                X   X   X   X   X
       Wait for Answer (@)                       X   X   X   X   X
       Fast Dial                             X       X       X   X


NOTE:  Depending on the &A setting, the following result codes
are enabled/disabled.  The default is &A1, /ARQ codes enabled.

 15   CONNECT 1200/ARQ
 16   CONNECT 2400/ARQ
 17   CONNECT 9600/ARQ

ZReset the modem to its NRAM settings; initiate new settings
of DIP switches 2-5 and 9.

+++  Escape code, preceded and followed by a guard time of at
least one second of no data transmission.  The modem
responds to +++ by returning to Command Mode and doing the
following:

 DIP Switch 9 DOWN (ON, Factory setting):
 Retains phone line connection
 Sends OK result code

 DIP Switch 9 UP (OFF):
 Hangs up
 Sends NO CARRIER result code

>Repeat the command continuously until canceled by pressing
<any key>.  If used in a Dial string, automated redialing
terminates after ten attempts.

/(Slash) Pause 125 milliseconds.

$Help command summary request.

&$   Help extended command summary request.

D$   Help Dial command summary request.

S$   Help S-register summary request.

<Ctrl>-S  Stop/restart display of Help screens.

<Ctrl>-C or <Ctrl>-K Cancel display of Help screens.


EXTENDED COMMAND SET

Command/Options Function

&An  Enable/disable /ARQ result codes.

&A0  /ARQ result codes disabled.

&A1  /ARQ result codes enabled (Default).

&Bn  Data Rate, terminal-to-modem (DTE/DCE).

&B0  DTE/DCE rate follows connection rate (Default).

&B1  DTE/DCE rate fixed at the DTE setting.  Allowable rates are 19.2k, 9600,
     7200, 4800, 2400, 1200, 300 bps.

&F   Load factory (ROM) settings into random access memory (RAM).

&Gn  Guard tone as part of answer sequence.

&G0  No guard tone, U.S., Canada (Default).

&G1  Reserved.

&G2  Guard tone, U.K., some Commonwealth countries.

&Hn  Transmit Data flow control.

&H0  Flow control disabled (Default).

&H1  Hardware (CTS) flow control.

&H2  Software (XON/XOFF) flow control.

&H3  Hardware and software control.

&In  Received Data software flow control.

&I0  Flow control disabled (Default).

&I1  XON/XOFF to local modem and remote computer.

&I2  XON/XOFF to local modem only.

&I3  Host Mode, Hewlett Packard protocol.

&I4  Terminal Mode, Hewlett Packard protocol.

&I5  XON/XOFF to remote modem for non-ARQ link flow control.

&Kn  Data compression enabled/disabled.

&K0  Disabled.

&K1  Auto enable/disable (Default).  Disabled if &B and &N rate settings are
     equal.

&K2  Enabled regardless of &B and &N settings.

&Mn  Normal or Error Control Modes.

&M0  Normal Mode.

&M1  Reserved.

&M2  Reserved.

&M3  Reserved.

&M4  Normal/ARQ Mode -- Normal if ARQ connection cannot be made (Default).

&M5  ARQ Mode -- hang up if ARQ connection cannot be made.

&Nn  Link Data Rate (DCE/DCE) variable or fixed.  With fixed link rate, modem
     hangs up if called or calling modem is operating at a different rate.

&N0  Variable link operations; negotiate highest possible link rate with
     remote modem (Default).

&N1  300 bps.

&N2  1200 bps.

&N3  2400 bps.

&N4  4800 bps.

&N5  7200 bps.

&N6  9600 bps.

&Pn  Pulse dialing make/break ratio.

&P0  U.S./Canada make/break ratio (Default).

&P1  U.K./some Commonwealth countries make/break ratio.

&Rn  Received Data hardware (RTS) flow control.

&R0  Reserved.

&R1  Ignore RTS (Default).

&R2  Received data output to terminal on RTS high; used only if terminal
     supports RTS.

&Sn  Data Set Ready (DSR) operations.

&S0  DSR override, always ON (Default).

&S1  Modem controls DSR.

&W   Write current settings to nonvolatile random access memory (NRAM).

&Yn  Break handling.  Destructive Breaks clear the buffer; expedited Breaks
     are sent immediately to the remote system.  Under data compression,
     destructive Breaks reset the local and remote modem's compression tables.

&Y0  Destructive, don't send Break.

&Y1  Destructive, expedited (Default).

&Y2  Nondestructive, expedited.

&Y3  Nondestructive, unexpedited; modem sends Break in sequence with data
     received from terminal equipment.

&Zn=s Write the following Dial string (s) to NRAM at position n (n=0-3).

&Zn? Display the phone number stored in NRAM at position n.


                APPENDIX D - PROBLEMS AND SOLUTIONS

You may occasionally encounter one of the problems listed here.
They are divided into two categories:  before and during the
exchange of user information over the data link.

-----------------------------------------------------------------
PROBLEM   SUGGESTED SOLUTION
-----------------------------------------------------------------
Before Establishment of the Data Link
-----------------------------------------------------------------

Your modem . . .

Doesn't answer the phone or go "off hook" to dial a number

Check to make sure your computer or terminal is sending a Data
Terminal Ready (DTR) signal via the RS-232C interface.  See
Appendix B-1 and Appendix B-3, DIP switch 1.

Doesn't respond OK when you type AT <Enter>

1.   Make sure you're typing in either upper case or lower case
letters, not a combination, and that you press the Enter
key.

2.   If you're using a computer, make sure it is in Terminal
Mode.

3.   Check to see that your terminal or software is set to the
correct bit rate and word length (7 bits with or without a
parity bit, or 8 bits and no parity).  If you're using a
computer, make sure your software is set to the correct
communications port.

4.   Check that DIP switch 3 is DOWN, for result code display,
and that DIP switch 2 is UP, for verbal result codes.  If
not, change the switch(es) and issue ATZ <cr>.  Or issue
whichever of these commands is needed:

 ATQ0 <Enter>   (to display the message)
 ATV1 <Enter>(to display a verbal message)

5.   Your machine may require the Carrier Detect override (DIP
Switch 6 DOWN), but you've changed the factory setting.
Check Appendix B-3.

6.   A rare condition is that your terminal/computer reverses the
send/receive functions at the RS-232C interface.  See
Appendix B-1, Appendix B-3, Quad switch, and your equipment
documentation.

-----------------------------------------------------------------
PROBLEM   SUGGESTED SOLUTION
-----------------------------------------------------------------
Before Establishment of the Data Link
-------------------------------------

Your computer . . .

Reacts as though a data link has been established, but no call
has been received

DIP Switch 6 is set DOWN at the factory for Carrier Detect
override, but your system may be reacting to improper signals
received at the RS-232C interface.  Set DIP switch 6 UP (OFF).

When the modem is in Answer Mode, acts as if a Carriage Return
has been entered, but nothing has been typed at the keyboard

Your software may be misreading signals from the modem as it
automatically sends a Carriage Return and a Line Feed before and
after the RING and CONNECT messages.  Entering the Quiet Mode
command, ATQ1 <cr>, should solve the problem.

Both modems . . .

Exchange carrier signals, but fail to establish a communications
link

1.   Check to make sure the proper bit rate, word length, parity
and number of Stop bits have been selected.

2.   If that doesn't correct the problem, it's likely that the
quality of the phone connection is poor and that the other
modem is missing the signals your modem is transmitting.
The variable quality of phone line connections may be due to
any number of conditions in the phone service's equipment or
the current environment.  Try several calls, and if you
still can't get through, try calling another modem.  If the
second modem accepts your call, the problem may lie with the
modem you first tried to call.

3.   Make sure the modem at the other end of the line is USR-HST
compatible at 9600 bps, V.22bis-compatible at 2400 bps, Bell
212A-compatible at 1200 bps, or Bell 103-compatible at 300
bps.  These are the common signaling standards for full
duplex dial-up network transmission in the U.S.

-----------------------------------------------------------------
PROBLEM   SUGGESTED SOLUTION
-----------------------------------------------------------------
During Data Transfer
-----------------------------------------------------------------

Your screen displays . . .

Only brackets

Check to make sure both modems are at the same bit rate, word
length, parity and number of Stop bits.  If the settings are
correct, the problem may be with the phone line.  Try the
following measures:

1.   Try placing the call again.  The phone company routes even
local calls differently each time you call.

2.   Try calling a different modem to see if the problem
persists.  (However, if it does, the problem may still be
with the phone line.)

3.   If you are using a long-distance service and the problem
persists, you might try using a different service.

Random (garbage) characters

Make sure both modems are set at the same bit rate, word length,
parity, and number of Stop bits.

Double characters

The modem's online local echo is probably ON.  Return the modem
to Command Mode (use +++) when it's convenient, and then type:

 ATF1 <Enter>

-----------------------------------------------------------------

IF YOU STILL HAVE PROBLEMS

The problems described above are by far the most common ones
that users encounter.  If the suggestions we've given don't clear
up your difficulties, try the following:

1.   Review the manual carefully to see if you've missed
something.

2.   Call or visit your dealer.  Chances are your dealer will be
able to give you the assistance you need.  This is much more
efficient and time-saving than returning the modem to
USRobotics.

3.   If your dealer can't clear up your difficulties, call the
USRobotics Technical Support Department at 800/982-5151 (in
Illinois, 312/982-5151).  Our Service Representatives will
be happy to give you assistance over the phone Monday
through Friday from 8:30 a.m. to 5 p.m. (Central Time Zone).

4.   If necessary, the Service Representative you talk to may
give you a Return Materials Authorization (RMA) number.
Modems without an RMA number will not be accepted.

5.   If you do return the modem to us, please follow this
procedure --

a.   Ship the unit, postage paid, in its original container.
 If the original container is not available, pack the
 modem carefully in a strong box of corrugated cardboard
 with plenty of packing material.

b.   Be sure to include your RMA number inside the package,
 along with your name and address.  Put your return
 address and your RMA number on the shipping label as
 well.

c.   Ship the well-packed modem to the following address.

   Technical Support Department
   USRobotics, Inc.
   8100 North McCormick Boulevard
   Skokie, Illinois 60076

d.   Please note that USRobotics will not accept packages
 sent COD, so be sure to send the modem postage paid.

e.   USRobotics will repair your modem and return it to you
 via United Parcel Service.


             APPENDIX E - ADDITIONAL OPERATIONAL INFORMATION

CONTENTS

E-1  Using Both Voice and Data Communications

E-2  High Speed/Low Speed Protocol

E-3  Retrain Sequence

E-4  PBX, Dedicated Line, and Leased Line Operations

E-5  Hewlett Packard 300 Installations

E-6  Analog Loopback and Other Testing


         APPENDIX E-1 - USING BOTH VOICE AND DATA COMMUNICATIONS

When you assemble the Courier, you have the option of plugging
your phone into the second modular jack of the modem so it's
available for voice calls.  You can also use the phone to
synchronize communications with another user whose modem uses the
AT command set, such as a USRobotics or USRobotics-compatible
modem.

PREPARATION

First call the other user to establish the bit rate, parity, word
length and number of Stop bits the other person's modem accepts.
Then both of you can turn the call over to your modems.

COMMANDS

1.   Without hanging up the phone, have your modem go off hook in
Originate Mode.  Type the following command:

 ATD <Enter>

NOTE:  Be sure the modem is not set to X2, X4, X6, or X7, or
it will return the NO DIAL TONE result code and hang up.

2.   The other party should then have the remote modem go off
hook in Answer Mode.  The following command is used to do
this:

 ATA <Enter>

3.   Now both of you can hang up your respective phones while the
two modems establish the data link.  They will maintain the
link until one of you gives your modem a command to
disconnect.

Either party's device can be the originate or answer modem:  it
doesn't matter who made the phone call.  But one modem must first
enter Originate Mode and the other then enter Answer Mode.  You
and the other party, therefore, must agree on which command, ATD
or ATA, you will each use.

NOTE:  It may happen that spurious garbage characters will
appear on the screen when you hang up the phone.  You can avoid
these by hanging up the phone as soon as you hear the modem go
off hook, during the one or two seconds it takes the two modems
to establish the link.


               APPENDIX E-2 - HIGH SPEED/LOW SPEED PROTOCOL

OVERVIEW

This appendix is intended for those users who want to try
programming their computers to switch bit rates to match the
Courier HST's connection rate.  The material here applies only
when the modem is set for variable rates at both the DTE
(computer) and link interfaces, &B0 and &N0, respectively.

In both Originate or Answer Modes, if the link rate is set to &N0
the Courier HST negotiates with the remote modem to connect at
the highest possible rate.  In addition, if the modem is set to
the Extended or Advanced result codes (X1 or higher) it signals
the DTE with one of the following result codes or, unless the
call is at 300 bps, an /ARQ Mode equivalent:

CONNECT(300 bps)
CONNECT 1200   (1200 bps)
CONNECT 2400   (2400 bps)
CONNECT 9600   (9600 bps)

The modem sends the result code at its previous rate.  Then it
switches to the new connection rate.

If your computer doesn't switch rates and you want to program it
to do so, use the example on the next page as a guide.  It
demonstrates the occurrence of the CONNECT codes in the
connection sequence, so that recognition of the codes can be used
to switch the computer.  The example uses a sequence of incoming
calls, but the codes apply to Originate Mode connections as well.

The example assumes the following settings:

Software: initially 9600 or 19.2k bps, allowing the full
   range of link rates:
   9600/7200/4800/2400/1200/300 bps

   Modem: X1 or higher (rate-specific CONNECT codes)
   &B0 (variable DTE rate)
   &N0 (variable link rate)

Example

-----------------------------------------------------------------
   Modem   DTE/DCE
Action  Response  Rate
-----------------------------------------------------------------
1.  Power on. 9600

2.  300-bps call comes in.   RING9600   CONNECT   9600

3.  Data link is established. 300   Data transfer takes place.

4.  Data session is over. NO CARRIER 300   Call is ended; loss of carrier.

5.  2400-bps call comes in.   RING300   CONNECT 2400   300

6.  Data link is established.2400   Data transfer takes place.

7.  Data session is over. NO CARRIER2400   Call is ended; loss of carrier.

8.  9600-bps call comes in.   RING2400   CONNECT 9600  2400

9.  Data link is established.9600   Data transfer takes place.

10. Data session is over. NO CARRIER9600   Call is ended; loss of carrier.
-----------------------------------------------------------------

Explanation

1.   The modem is powered on and is operating at 9600 bps.  If
the software is then set to 19.2k bps and an AT command
sent, the DTE/DCE rate would be 19.2k bps.

2.   A 300-bps modem calls.  The Courier senses the incoming
signal and sends the messages RING and CONNECT to the
computer.  These messages are sent at 9600 (or 19.2k) bps,
the current rate.

3.   Since the Courier responds CONNECT, rather than CONNECT
1200, 2400, or 9600, the computer switches to 300 bps.  The
modem automatically shifts to 300 bps to accept the data
from the incoming call.

4.   The 300-bps data session is terminated; the modem sends the
message NO CARRIER at 300 bps.

5.   A 2400-bps call comes in.  The modem responds RING and
CONNECT 2400.  These message are sent at the current bit
rate of 300 bps.

6.   The computer, receiving the CONNECT 2400 message, adjusts
accordingly to the higher bit rate.  The modem also shifts
to 2400 bps.

7.   The 2400-bps data session is terminated; the modem sends the
message NO CARRIER at 2400 bps.

8.   A 9600-bps call comes in.  The modem responds RING and
CONNECT 9600.  These message are sent at the current bit
rate of 2400 bps.

9.   The computer, receiving the CONNECT 9600 message, adjusts
accordingly to the higher bit rate.  The modem also shifts
to 9600 bps.

10.  The 9600-bps data session is terminated; the modem sends the
message NO CARRIER at 9600 bps.

NOTE:  If online fallblack occurs during a 9600-bps call, the
modem does not send CONNECT result codes for 7200- or 4800-bps
link rates.

Keep in mind that whether or not your computer adjusts to these
rate changes, the Courier automatically shifts to the connection
rate if it is set to &B0.


                  APPENDIX E-3 - RETRAIN SEQUENCE

DESCRIPTION

The retrain sequence occurs at 2400 and 9600 bps.  It is a
resynchronization sequence performed when one of the connected
modems senses that problems on the line may affect data
reliability.  The procedure is essentially transparent to users.

The following is an example of retrain events:

1.   The Courier HST's receiver, sensing a need to retrain,
clamps RX to MARKs.

2.   The remote modem, after receiving about 100 ms of analog
signals (a pattern of ?~?~ is usually output), clamps RX
data to MARKs.

3.   After the training sequence, approximately one second, the
Courier unclamps RX data and turns HS ON.

4.   The remote modem reenters Data Mode.


     APPENDIX E-4 - PBX, DEDICATED LINE, AND LEASED LINE OPERATIONS

The following operations apply in installations where the modem
is not directly connected to the public-access switched telephone
network.

PBX Installations

It's possible to install the modem(s) on the customer side of an
analog PBX.  When used with multiple telephones per line, DIP
switch 7 can be set DOWN to short A/A1 when the modem is off
hook.  This notifies other devices sharing the line that the line
is busy.

Calling an Outside Party

To have the modem make an outside call, follow the auto-dial
instructions in Chapter 6, but insert the sequence used to obtain
an outside line, followed by a comma, before the phone number in
the Dial command.

The off-hook indicator on the PBX should show the extension as
busy if DIP switch 7 is DOWN.

Internal Calling

To call another modem on the PBX system, use the Dial command
described in Chapter 6 with the extension of the destination
modem.  If set to Auto Answer, the called modem automatically
answers on the incoming ring.

The off-hook indicators on the PBX should show both extensions as
busy if DIP switch 7 is DOWN on both modems.

2-Wire Dedicated (Private) or Leased Line

A 2-Wire dedicated (private) line is a customer-installed,
twisted-pair line.  2-Wire leased lines are provided by the
telephone company and may be designated as 2-Wire 3002 Analog
Circuits.

In both types of installation there is a continuous point-to-
point connection between two modems.  For optimal operations, the
physical length of the line should not exceed 5 miles.

To establish the connection, follow these steps:

1.   Decide which modem is to be the Originate modem and which
the Answer modem.  The originate and answer frequencies must
be defined for the modems to communicate.

2.   First put the calling modem in Originate Mode with the
manual Dial command:

 ATD <Enter>

NOTE:  Be sure the modem is not set to X2, X4, X6, or X7, or
it will return the NO DIAL TONE result code and hang up.

3.   Then put the answering modem in Answer Mode with the manual
Answer command:

 ATA <Enter>

NOTE:  If there is an interruption in the communications link (a
strike to the line due to weather or some other problem), repeat
steps 2 and 3 to reestablish the link.


          APPENDIX E-5 - HEWLETT PACKARD 3000 INSTALLATIONS

The Courier HST recognizes the ASCII ENQ/ACK characters exchanged
between the Hewlett Packard 3000 host computer and its terminals.
The HP host sends the terminal an ENQ character at predefined
intervals, and sends no more data until the terminal responds
with an ACK character.

Courier HST modems manage this ENQ/ACK protocol so that
communication is speeded up, thereby enabling HP terminals to
achieve high speeds on dial-up lines.  Special Received Data flow
control settings (the &I command) are required for HP users.

Follow these guidelines:

1.   Use one of the &I settings given here for both Normal and
error control (ARQ) sessions, i.e., for all &M settings.

2.   Do not use a software setting for Transmit Data flow
control.  Set the modem only to &H0 or &H1, according to the
guidelines in Chapter 4.

3.   Set the Courier HST to Host Mode if it is attached to the
host computer, or to Terminal Mode if it is attached to a
terminal:

Host Mode  AT&I3 <Enter>
Terminal Mode  AT&I4 <Enter>


           APPENDIX E-6 - ANALOG LOOPBACK AND OTHER TESTS

ANALOG LOOPBACK SELF-TEST

This test is a way to check that the modem's transmitter and
receiver are working properly.  During Analog Loopback, data from
the computer is sent in a loop through the transmitter (where it
is modulated) and the receiver (where it is demodulated), and
returned to the screen.  Due to asymmetrical modulation at 9600
bps, the test must be performed at 2400 bps or below.

You can use the modem's internal test pattern as data, or type
your own at the keyboard.  Follow these procedures to test the
modem by sending the test pattern:

NOTE:  If the modem is set to X2, X4 X6, or X7 it will return the
NO DIAL TONE result code and hang up.  Send the modem a different
X setting.

1.   Set your terminal or software to 2400 bps and send the modem
the following command, which has the results listed below.

 AT &M0 S16=5D <Enter>

&M0 Sets the modem to Normal Mode.  If the modem is set
 for error control (&M4 or &M5) you can't tell if
 there is a problem because the modem checks for
 errors and automatically retransmits any errored
 data.
S16=5   Sets S-Register 16 to Analog Loopback with test
 pattern.  The modem sends, modulates and demodulates
 its internal test pattern and returns that pattern
 to your screen.
D   The Dial command selects testing the Originate
 (Dial) frequency.  The Answer command (A) tests the
 Answer frequency.

The modem enters Analog Loopback Mode, goes off hook, sends
the message CONNECT 2400 to the screen, and then sends the
test pattern.

2.   When you're satisfied with the test, terminate the operation
by pressing any character key on the keyboard.  The modem
goes back on hook and responds with the message NO CARRIER.

3.   Reset the error control default and reset S-Register 16 to
zero, for data operations, by entering this command:

 AT &M4 S16=0 <Enter>

Normal/Test Frequencies

In normal operations, communicating modems transmit at different
frequencies within the communications channel, one low and the
other high.  The calling modem is said to be in Originate Mode:
it transmits at the low (Originate) frequency and receives at the
high  frequency.  The answering modem, in Answer Mode, transmits
at the high (Answer) frequency, and receives on the low
frequency.

During Analog Loopback testing, the modem transmits and receives
on the same frequency, either Originate (low) or Answer (high).
The Analog Loopback command in the previous section tests the
Originate frequency.

Testing the Answer Frequency

To test the Answer frequency, substitute the Answer command, A,
as follows:

 AT &M0 S16=5A

ADDITIONAL TESTS

In all, S-register 16 has five settings, as follows.

0Data Mode (normal operations)
1Analog Loopback
2Dial Test
4Test Pattern
5Analog Loopback with Test Pattern

NOTE:  After any testing, be sure to reset S-register 16 for Data
Mode, with or without the default error control setting (&M4):

 AT &M4 S16=0 <Enter>

S16=1

1.   Select this option to perform analog loopback testing by
sending your own data instead of the test pattern.  Use
either of the following commands after setting your terminal
or software to 2400 bps.  If the modem is set for error
control, insert &M0 before the S16 command.

 ATS16=1D <Enter>
 ATS16=1A <Enter>

2.   When the modem displays the message CONNECT 2400, type any
message you wish at the keyboard.  It is looped through the
modem and returned to the screen.

3.   End the test by not typing anything for at least one second
and then typing the escape code that brings the modem back
to Command Mode.  (Do not type the AT prefix or press the
Enter key.)

 +++

4.   The modem returns the OK message. Reset the error control
default and reset S-Register 16 to zero, for data
operations, by entering this command:

 AT &M4 S16=0 <Enter>

S16=2

The Dial Test is used for factory testing the frequencies of
Touch-Tone values.  When S-register 16 is set to 2 and a single
Touch-Tone is dialed (e.g., ATD7), the modem continues to
transmit that tone until another Carriage Return is entered.

S16=4

The Test Pattern alone is used for testing equipment and the
phone line.  If S16 is set to 4 and a Dial command issued, the
Courier transmits the test pattern upon connection to the remote
system.  If set for Auto Answer the Courier transmits the test
pattern when it answers a call.  Be sure to reset S16 to zero for
normal calls.

Testing at 1200 BPS

To test the modem at 1200 bps, follow the previous instructions,
but first set your software to 1200 bps.

Testing at 300 BPS

The Test Pattern is not available at 300 bps.  Analog Loopback
testing is done at 300 bps by setting your software to 300 bps
and setting S-16 only to 1D or 1A.

NOTE:  It might happen that you have issued either S16=1 or 5 and
the modem is in Analog Loopback Mode, but you haven't yet sent a
Dial or Answer command to initiate testing.  If the modem is also
set for Auto Answer and a call comes in, the Courier resets S16
to zero and answers the call.


              APPENDIX F - TECHNICAL SPECIFICATIONS

Compatibility

USR-HST, 9600 bps, asynchronous, asymmetrical (9600/450 bps with
automatic handshake adjustment to 300-bps), trellis-coded
modulation, Quadrature Amplitude Modulation (QAM)

USR-HST, 7200 bps, asynchronous, asymmetrical (9600/450 bps with
automatic handshake adjustment to 300-bps), trellis-coded
modulation, Quadrature Amplitude Modulation (QAM)

USR-HST, 4800 bps, asynchronous, asymmetrical (9600/450 bps with
automatic handshake adjustment to 300-bps), unencoded Quadrature
Amplitude Modulation (QAM)

CCITT recommendation V.22bis, 2400 bps, asynchronous, Quadrature
Amplitude Modulation (QAM)

Bell 212A, 1200 bps, asynchronous, Differential Phase Shift
Keying (DPSK)

Bell 103, 300 bps, asynchronous, Frequency Shift Keying (FSK)

Microcom Networking Protocol (MNP), Service Levels 1-5 at
2400/1200 bps

USRobotics proprietary HST protocol at 9600/7200/4800 bps,
similar to MNP Levels 1-5, adapted for asymmetrical modulation

RS-232C terminal/modem interface

Superset of industry standard AT command set, S-registers, DIP
switches

Online data rate fallback

7200, 4800 bps

Phone Line Interface

RJ11, RJ12, RJ13, RJ41, RJ45 phone jacks

Communications Channel

Full/half duplex on 2-wire dial-up, dedicated, or leased phone
lines, demand-driven high speed channel turnaround

Data Rates

300, 1200, 2400, 4800, 7200, 9600 bits per second

Operational Modes

Auto Dial/Answer, Manual Originate/Answer

Dialing

Rotary (pulse 0-9), Touch-Tone (DTMF 0-9, #, *), a-z when in
Quote (") Mode

Data Format

Binary, serial, asynchronous; defaults to 7-bit word length, even
parity

            Start      Data                          Stop
             Bits      Bits          Parity          Bits
              1         7          Even, Odd          1
                                  Mark, Space
              1         7       None, Even, Odd,      2
                                  Mark, Space
              1         8             None           1, 2


Front Panel Indicators

HS   High Speed (9600 bps)
AA   Auto Answer/Answer
CD   Carrier Detect
OH   Off Hook
RD   Receive Data
SD   Send Data
TR   Terminal Ready (DTR)
MR   Modem Ready/Power
RS   Request to Send
CS   Clear to Send
ARQ  Error control connection established
AL   Analog Loopback Self-Test

Programmable S-Registers

Values in parentheses are defaults:

Number of rings on which to answer (1)
ASCII character definitions, decimal: escape code (43), Carriage
Return (13), Line Feed (10), Backspace (8)
Timing: Wait before dialing (2 sec)
Carrier Detect wait (30 sec)
Pause in Dial, Repeat commands (2 sec)
Remote Carrier Detect before local recognition (0.6 sec)
Disconnect at loss of carrier (0.7 sec)
Escape code guard time (1 sec)
Touch-Tone duration, spacing (70 Ms)
Break length, to DTE (100 Ms)
Disable MNP Levels 3, 4
Disable 450-bps back channel, force 300 bps
Optional non-error control Transmit buffer size
Auto Dial stored phone number on DTR, reset or power on
Answer in Originate Mode
Modem self-testing (0, Data Mode)
Inactivity Timer (0, disabled)

Switch Functions

Externally accessible.  Values in parentheses are factory
settings:  UP = OFF (open), DOWN = ON (closed).

Volume control
DTR override (DOWN)
Result code mode (UP, verbal)
Result code display (DOWN, displayed)
Command Mode echo (UP, echo ON)
Auto Answer (DOWN, AA suppressed)
CD override (DOWN)
RJ11/RJ13 jack (UP, RJ11)
Smart/Dumb mode (DOWN, Smart)
Online Escape code with/without disconnect (DOWN, no
disconnect)
Load NRAM defaults/ROM factory settings (UP, NRAM)
RS-232C Modem/Terminal data interface (UP, normal
assignments of Pins 2 and 3)

Flow Control Buffers

Transmit Buffer:

Error control:  3.5k bytes
Non-Error control:  1.5k bytes, 128-byte option

Receive Buffer:  2k bytes

Command Buffer

40 characters, exclusive of AT prefix, Carriage Return and spaces

Control Commands

User-programmable nonvolatile memory (NRAM)
Data compression
Fixed/variable DTE and link rates
Error control
Error control result codes
Transmit data flow control (hardware, software)
Received data flow control (hardware, software)
Command mode, online echoing
Verbal/numeric result codes
Standard, Extended, Advanced result code sets
Result code display ON/OFF
Speaker OFF, ON until CD, ON through CD and data transmission, ON
after last digit dialed until CD
Command Mode/online toggle
Voice/data communications
Adaptive dialing
Fast dialing, search for dial tone
Wait for second dial tone, then continue
Wait for answer, then continue
Dial alphabetic string
Dial one of four phone numbers stored in NRAM
Flash switch-hook to transfer call
Reset to NRAM defaults
Load ROM factory settings
Request to Send (RTS) override
Data Set Ready (DSR) override
Break handling

Test Options

Analog loopback (2400/1200/300 bps)
Dial test
Test pattern (2400/1200 bps)
Analog loopback with test pattern (2400/1200 bps)

Call Progress Codes

NO DIAL TONE
BUSY
NO ANSWER
RINGING
VOICE

Equalization

Adaptive

Transmitter Carrier Frequencies

USR-HST
  Originate Mode:   350 Hz
 Answer Mode:   1800 Hz
V.22bis, Bell 212A
  Originate Mode:   1200 Hz
 Answer Mode:   2400 Hz
Bell 103
  Originate Mode:
 Mark:   1270 Hz
Space:   1070 Hz
 Answer Mode:
 Mark:   2225 Hz
Space:   2025 Hz

Receiver Carrier Frequencies

USR-HST
  Originate Mode:   1800 Hz
 Answer Mode:350 Hz
V.22bis, Bell 212A
  Originate Mode:   2400 Hz
 Answer Mode:   1200 Hz
Bell 103
  Originate Mode:
 Mark:   2225 Hz
Space:   2025 Hz
 Answer Mode:
 Mark:   1270 Hz
Space:   1070 Hz

Certification

FCC Part 68 & Part 15, Subpart J, Class B Domestic; DOC (Canada)

Power Adapter

UL listed, CSA approved, Supply voltage:  115 VAC, 60 Hz, 16 VAC
Output

Power Consumption

10 watts

Failed Call Timeout

30-sec. default, programmable 2-255 sec.

Answer Tone Timeout

30 sec.

Answer Tone Detector

2150-2300 Hz

Loss of Carrier Timeout

(Disconnect Timer) 0.7-sec. default, programmable 0.2-25.5 sec.

Receive Sensitivity

-43 dBm

Transmit Level

- 9 dBm

Transmitter Frequency Tolerance

.01 %

Size

8.30 x 12.65 x 1.57 inches


                               GLOSSARY

Cross-references in the following definitions are printed in
boldface.

Analog Loopback

A modem self-test in which data from the keyboard is sent to the
modem's transmitter, modulated into analog form, looped back to
the receiver, demodulated into digital form, and returned to the
screen for verification.  Tests either the modem's originate or
answer frequency.

Analog signals

Continuous, varying waveforms such as the voice tones carried
over phone lines.  Contrast with digital signals.

Answer Mode

A state in which the modem transmits at the pre-defined high
frequency of the communications channel and receives at the low
frequency.  The transmit/receive frequencies are the reverse of
the calling modem which is in Originate Mode.

ARQ

Automatic Repeat Request.  A general term for error control
protocols which feature error-detection and automatic
retransmission of defective blocks of data.  See HST and MNP.

ASCII

American Standard Code for Information Interchange.  A 7-bit
binary code (0s, 1s) used to represent letters, numbers, and
special characters such as $, !, and /.  Supported by almost
every computer and terminal manufacturer.  See Appendix B-6 for
decimal and hexadecimal code equivalents.

Asynchronous Transmission

Data transmission in which the length of time between transmitted
characters may vary.  Because the time lapses between transmitted
characters are not uniform, the receiving modem must be signaled
as to when the data bits of a character begin and when they end.
The addition of Start and Stop bits to each character serves this
purpose.  Compare Synchronous Transmission.

Auto Answer

A feature in modems enabling them to answer incoming calls over
the phone lines without the use of a telephone receiver.

Auto Dial

A feature in modems enabling them to dial phone numbers over the
phone system without the use of a telephone transmitter.

Baud Rate

The number of discrete signal events per second occurring on a
communications channel.  Although not technically accurate, baud
rate is commonly used to mean bit rate.

Binary Digit

A 0 or 1, reflecting the use of a binary numbering system (only
two digits).  Used because the computer recognizes either of two
states, OFF or ON.  Shortened form of binary digit is "bit."

Bit Rate

The number of binary digits or bits transmitted per second (bps).
Communications channels using telephone channel modems are
established at set bit rates, commonly 110, 300, 1200, 2400,
4800, 9600, and 144000.

BPS

The bits (binary digits) per second rate.

Buffer

A memory area used as temporary storage during input/output
operations.  Two examples in the Courier HST are the command
buffer (last issued command) and the flow control buffer (for
data flow control and storing copies of transmitted frames until
they are positively acknowledged by the receiving modem).

Byte

A group of binary digits stored and operated upon as a unit.  A
byte may have a coded value equal to a character in the ASCII
code (letters, numbers), for example, or have some other value
meaningful to the computer.  In user documentation, the term
usually refers to 8-bit units or characters.  1 kilobyte = 1,024
bytes or characters; 64k = 65,536 bytes or characters.

Carrier

A continuous frequency capable of being either modulated or
impressed with another information-carrying signal.  Carriers are
generated and maintained by modems via the transmission lines of
the telephone companies.


                        COURIER 1200

CCITT

An international organization that defines standards for
telegraphic and telephone equipment.  For example, the Bell 212A
standard for 1200 bps communication in North America is observed
internationally as CCITT V.22.  For 2400 bps communication, most
U.S. manufacturers observe V.22bis.  The initials CCITT represent
the French name; in English it's known as the International
Telegraph and Telephone Consultative Committee.

Character

A representation, coded in binary digits, of a letter, number, or
other symbol.

Characters Per Second

A data transfer rate generally estimated from the bit rate and
the character length.  For example, at 2400 bps, 8-bit characters
with Start and Stop bits (for a total of ten bits per character)
will be transmitted at a rate of approximately 240 characters per
second (cps).  Some protocols, such as USR-HST and MNP-Service
Class 3, employ advanced techniques to increase cps.  When the
Courier HST is set for maximum throughput, as described in
Chapter 3, 140 characters in addition to the standard 960 can be
transmitted for a total of 1100 cps.

Cyclic Redundancy Checking (CRC)

An error-detection technique consisting of a cyclic algorithm
performed on each block or frame of data by both sending and
receiving modems.  The sending modem inserts the results of its
computation in each data block in the form of a CRC code.  The
receiving modem compares its results with the received CRC code
and responds with either a positive or negative acknowledgment.
In the ARQ protocol implemented in the Courier HST, the receiving
modem accepts no more data until a defective block is received
correctly.

Data Communications

A type of communications in which computers and terminals are
able to exchange data over an electronic medium.

Data Compression Table

A table of values assigned for each character during a call under
data compression.  Default values in the table are continually
altered and built during each call:  the longer the table, the
more efficient throughput gained.

If a destructive Break is sent during a call (see the &Y
command), causing the modems to reset the compression tables, you
can expect diminished throughput.

DCE

Data Communication (or Circuit-Terminating) Equipment.  In this
manual, the dial-up modems that establish and control the data
link via the telephone network.

Dedicated Line

A user-installed telephone line used to connect a specified
number of computers or terminals within a limited area, for
example, one building.  The line is a cable rather than a public-
access telephone line.

Default

Any setting assumed, at startup or reset, by the computer's
software and attached devices, and operational until changed by
the user.

Digital Signals

Discrete, uniform signals.  In this manual, the term refers to
the binary digits 0 and 1.

DTE

Data Terminal (or Terminating) Equipment.  The device, such as a
personal computer, terminal, or mainframe, that generates or is
the final destination of data.

Duplex

Indicates a communications channel capable of carrying signals in
both directions. See Half Duplex, Full Duplex.

Equalization

A compensation circuit designed into modems to counteract certain
distortions introduced by the telephone channel.  Two types are
used:  fixed (compromise) equalizers and those that adapt to
channel conditions.

Error Control

Various techniques which check the reliability of characters
(Parity) or blocks of data.  The Courier's error control protocol
provides error control through error detection (CRC) and
retransmission of errored frames (ARQ).

Flow Control

A mechanism that compensates for differences in the flow of data
input to and output from a modem or other device.

Frame

A data communications term for a block of data with header and
trailer information attached.  The added information usually
includes a frame number, block size data, error-check codes, and
Start/End data.

Full Duplex

Signal flow in both directions at the same time. In microcomputer
communications, may refer to the suppression of the online Local
Echo.  The receiving computer may provide a Remote Echo.

Half Duplex

Signal flow in both directions, but only one way at a time.  In
microcomputer communications, may refer to activation of the
online Local Echo, which causes the modem to send a copy of the
transmitted data to the screen of the sending computer.

HST

High Speed Technology, part of the trademark for USRobotics' USR-
HST, a proprietary signaling scheme, design and protocol for 9600
bps modems.  USR-HST incorporates trellis-coded modulation, for
greater immunity from variable phone line conditions, and asym-
metrical modulation for more efficient use of the phone channel.
HST also represents the enhanced error control protocol at 9600
bps that is similar to and compatible with MNP error control at
2400/1200 bps.

Local Echo

A modem feature that enables the modem to send copies of keyboard
commands and transmitted data to the screen.  When the modem is
in Command Mode (not online to another system) the local echo is
invoked through the ATE1 command.  The command causes the modem
to display your typed commands.  When the modem is online to
another system, the local echo is invoked through the ATF0
command.  This command causes the modem to display the data it
transmits to the remote system.

MNP

Microcom Networking Protocol.  An error control protocol
developed by Microcom, Inc. and now in the public domain.  The
protocol ensures error-free transmission at 1200 and 2400 bps
through error detection (CRC) and retransmission of errored
frames.

Modem

A device that transmits/receives computer data through a
communications channel such as radio or telephone lines.  The
Courier is a telephone channel modem that modulates, or
transforms, digital signals from a computer into a form that can
be carried successfully on a phone line.  It also demodulates
signals received from the phone line back to digital signals
before passing them to the receiving computer.

Intelligent modems with built-in software, such as the USRobotics
modem described in this manual, simplify using phone networks for
data communications.

Nonvolatile Memory (NRAM)

User-programmable random access memory whose data is retained
when modem power is turned off.  Used in the Courier HST to store
a user-defined default configuration loaded into random access
memory (RAM) at power on.

OFF/ON Hook

Modem operations which are the equivalent of manually lifting a
phone receiver (taking it off hook) and replacing it (going on
hook).

Originate Mode

A state in which the modem transmits at the pre-defined low
frequency of the communications channel and receives at the high
frequency.  The transmit/receive frequencies are the reverse of
the called modem which is in Answer Mode.

Parallel Transmission

The transfer of data characters using parallel electrical paths
for each bit of the character, for example, 8 paths for 8-bit
characters.  Data is stored in computers in parallel form, but
may be converted to serial form for certain operations.  See
Serial Transmission.

Parity

An error-detection method that checks the validity of a
transmitted character.  Character checking has been surpassed by
more reliable and efficient forms of block-checking, including
XMODEM, a public domain protocol used in some telecommunications
software, and the ARQ protocol implemented in the Courier HST.

The same type of parity must be used by two communicating
computers, or both may omit parity.  When parity is used, a
parity bit is added to each transmitted character.  The bit's
value is 0 or 1, to make the total number of 1s in the character
even or odd, depending on which type of parity is used.

Protocol

A system of rules and procedures governing communications between
two or more devices.  Protocols vary, but communicating devices
must follow the same protocol in order to exchange data.  The
format of the data, readiness to receive or send, error
detection, and error handling are only a few of the operations
that may be defined in a protocol.

RAM

Random Access Memory.  Memory that is available for use when the
modem is turned on and clears of all information when the power
is turned off.  The Courier HST's RAM holds the current
operational settings, a flow control buffer, and a command
buffer.

Remote Echo

A copy of the data received by the remote system, returned to the
sending system and displayed on the screen.  Remote echoing is a
function of the remote system.

ROM

Read Only Memory.  Permanent memory, not user-programmable.  The
Courier HST's factory settings are stored in ROM and can be read
(loaded) into RAM as an operational configuration.

Serial Transmission

The transfer of data characters one bit at a time, sequentially,
using a single electrical path.  See Parallel Transmission.

Start/Stop Bits

The signaling bits attached to a character before the character
is transmitted during Asynchronous Transmission.

Synchronous Transmission

A form of transmission in which groups of data bits are sent at
regular intervals.  Because the timing is uniform, no Start or
Stop bits are required.  See Asynchronous Transmission.

Terminal

A device whose keyboard and display are used for sending and
receiving data over a communications link.  Differs from a
microcomputer in that it has no internal processing capabilities.
Used to enter data into or retrieve processed data from a system
or network.

Terminal Mode

An operational mode required for microcomputers to transmit data.
In Terminal Mode the computer acts as if it were a standard
terminal such as a teletypewriter, rather than a data processor.
Keyboard entries go directly to the modem, whether the entry is a
modem command or data to be transmitted over the phone lines.
Received data is output directly to the screen.  The more popular
communications software products control Terminal Mode as well as
enable more complex operations, including file transmission and
saving received files.

Throughput

The amount of actual user data transmitted per second without the
overhead of protocol information such as Start and Stop bits or
frame headers and trailers.  Compare characters per second.

Transmission Rate

Same as Bit Rate.

V.22bis

The international CCITT standard for modem communications at 2400
bps.  The standard includes an automatic data rate fallback to
1200 bps and compatibility with Bell 212A/V.22 modems.

Word Length

The number of bits in a character without parity, start or stop
bits.

XON/XOFF

Standard ASCII control characters used to tell an intelligent
device to stop/resume transmitting data.  In most systems typing
<Ctrl>-S sends the XOFF character.  Some devices, including the
Courier, understand <Ctrl>-Q as XON; others interpret the
pressing of any key after <Ctrl>-S as XON.


                            INDEX

A/A1 shorting, DIP switch 7, B-3.2, E-4.1
ACK character, HP installations, App. E-5
Adaptive dialing, 1-3, 5-4, 63
Advanced result code set, 5-3--5-5
Analog loopback self-test, App. E-6
Answer mode
auto answer, 6-9--6-10
rate recognition, 4-8, App. E-2
manual answer, E-1.1, E-4.1
ARQ (Automatic Repeat Request)
CONNECT result codes (&A), 5-5
definition, 4-1, A-3
flow control requirement, 3-2, 4-5
mode select (&M), 3-1, 4-3--4-4
operations, A-1--A-4
timeout, retransmit maximum, 4-2
with Auto Answer, 4-4
Assembly, modem, 2-2--2-4
RS-232C cable requirements, 2-2, App. B-1
Aymmetrical modulation, 1-1, 3-2--3-3
Asterisk (*), 6-2
Asynchronous transmission, F-1, Glossary
ASCII Chart, App. B-6
character definitions, 5-8, B-5.1
Audio monitor (speaker), 5-6--5-7
Auto dialing, 6-1--6-8
Help screen (D$), 7-6
quick reference, 3-1
stored phone numbers, 3-3, 6-7
Auto answering, 6-9
disabling, 6-10
number of rings on which to answer (S0), 7-3, B-5.1
with Dip switch 5, 6-9, B-3.1
Automatic Repeat Request, see ARQ

Back channel, 3-2, F-1
Backspace key, ASCII definition (S5), B-5.1
Baud rate, Glossary
Bits per second (bps),
defined,  Glossary
link negotiation, 3-3, 4-8, A-1-A-3
online fallback, 1-2, 4-3, F-1
rate recognition, 4-8, 6-1, App. E-2
setting the, 3-1, 3-2, 4-8-4-9, 6-1
Break handling (&Y), 5-8
Break length, modem to terminal (S21), B-5.4
Buffers
command, 6-7
flow control, 3-2, 4-5, A-4
Busy answer, 3-4, 5-4, 6-6--6-7

Calling another modem, 3-1, 6-1--6-8
at another extension, E-4.1
Call duration reporting (K), 5-7
Call progress messages, 5-3, 5-4--5-5
Canadian certification (DOC), ix, 6-7
Carrier, defined, 5-6
Carrier Detect (CD) override (DIP switch 6), 2-5, B-3.2, D-1
CCITT
answer tone (B), 6-10
defined, Glossary
Channel, turnaround, 1-1, 3-2, F-1
Characters per second (cps), 1-1, A-2--A-3
maximum throughput, 3-2, 4-1--4-2, 4-9
Clear to Send (CTS), 4-5, B-1.1
Clock, Courier (K), 5-7
Command length, C-1
Command mode local echo (E), 2-5, 5-
Command summary, App. C
Commands
Adaptive dialing (X2-X6), 6-
Alphabetical listing, App. C
Answer mode, manual (A)
 analog loopback self-test, 2-6
 on dedicated or leased lines, E-4.1
 with voice/data operations, E-1.1
ARQ mode select (&M), 3- , 4- , 6-
ARQ result codes (&A), 5-4
AT (attention), 2-
Break handling (&Y), 5-
Cancel dialing (any key), 6-
Carriage return (<Enter>), 2-
 ASCII definition (S3), B-5.1
 to enter commands, 2-
Comma (pause), 6-
Command mode local echo (E), 2- , 5-
Compression, data (&K), 3-1, 4-4, 4-5, A-2--A-3
Data rate select, 3-1, 3-2, 4-9, 6-1
 DTE rate (&B), 4-
 Link rate (&N), 4-
Data set ready, DSR (&S), 4-10
Dial (D), 3-1, 6-2--6-8
 and return to command state (;), 6-
 letter strings ("), 6-
 Help screen (D$), 6-
 stored phone number (DS), 6-
Disable transmitter (C), 5-7
Disconnect (H, +++), 6-
Duplex, 5-
Echo, local (E, F), 2-5, 5-
Escape code (+++), 3- , 6-
Factory settings, loading (&F), 5-
Flow control, 3- , 4-
 received data (&I, &R), 4-
 transmit data (&H), 3- , 4-
Hang up (H, +++), 6-
 ARQ mode (+++), 3- , 6-
Help screens, using, 7-4
 ampersand commands (&$), 7-
 basic commands ($), 7-
 dialing (D$), 7-
 S-register functions (S$), 7-
Inquiry options (I), 7-
 call-duration (I3), 5- , 7-
 current settings display (I4), 7-
 link diagnostics display (I6), 7-
 NRAM settings display (I5), 3-3, 5-1, 7-
Local echo (E, F), 2-5, 5-
MNP mode select (&M), 3- , 4-
Online local echo (F), 5-
Pulse dial make/break ratio (&P), 6-
Pulse/Touch-Tone dial (P/T), 6-
Quiet mode (Q), 5-
Receive only, disable transmitter (C), 5-
Received data flow control (&I, &R), 4-
Redial/re-execute previous command
 one time (A/), 3- , 6-
 continuous, (A>), 3- , 6-
Repeat, continuous (>), 3- , 6-
Reset to NRAM defaults (Z), 5-
Response modes (V), 5-
Result code sets (X), 5-
Return online after +++ (O), 6-
Reverse frequencies (R), 6-
Save in NRAM
 modem settings (&W), 5-
 phone numbers (&Zn=s), 5-
Settings status display
 current settings (I4), 7-
 NRAM settings (I5), 3-3, 5-1, 7-
Speaker control (M), 5-
S-register settings (Sr=n), B-5.1
 query specific register (ATSr?), 4- , 7-
Touch-Tone/pulse dial (P/T), 6-
Transfer call (!), 6-
Transmit data flow control (&H), 3-1, 4-
Verbal/numeric response modes (V), 5-
Wait for second dial tone (W), 6-
Wait for answer (@), 6-
Write to NRAM
 modem settings (&W), 5-
 phone numbers (&Zn=s), 5-
Compatibility, 1- , 6-1, F-1
error control, 3- , 4-
Compression, see Data compression
Computer interface (DTE) speed select (&B), 4-
Configuration, general
DIP switches, 2-4, App. B-3
factory defaults, 5-2, App. B-4
interface controls, Ch. 4
internal controls, Ch. 5
NRAM options, 5-1, B-4
physical assembly, 2-2--2-4
S-registers, App. B-5
Configuration to call:
HST-compatibles, 3-
MNP-compatibles, 3-
non-MNP compatibles, 3-
CONNECT messages, 5- , 6- , App. E-2
ARQ (&A), 5-
Connection rate, 4- , E-2.1
negotiation, 3- , 4- , E-2.1
Connectors, DTE interface
requirements, 2-
physical assembly, 2-4
RS-232C interface definitions, App. B-1
CRC, cyclic redundance checking, A-
CTS, 4-5, B-1.1
Customer service, USRobotics, ii, D-4

Data compression (&K), 1-1, 3-1, 3-2, 4-4, 4-5, A-3
Data format, 6- , F-1
Data rate
link negotiation, 3-3, 4-8--4-9, App. E-2
online fallback, 1-2, 4-3, E-2.3, F-1
setting the, 3-1, 3-2, 4-8--4-9, 6-1
Data rate select (&B, &N), 4-8--4-9
Data Set Ready (DSR, &S), 4-10, B-1.1
Data Terminal Ready (DTR, DIP switch 1), 2- , B-1.1, B-3.1,
 D-1
DCE, defined, 4-1
Defaults
commands, App. C
NRAM/factory, App. B-4
Diagnostics
call, link, 7-3
testing, 2-5, 7-1, App. E-6
Dial, auto
at a glance, 3-
commands, functions, 6-2--6-8
stored phone number (DSn), 3- , 6-
Dialing type
adaptive, 1-3, 5-4, 6-3
pulse/tone, 6-
Department of Communications (DOC), xi, 6-
Digital signals, Glossary
DIP switches, 2-4, App. B-3
auto answer, 6-
CD override, D-1, D-2
disconnect/hang up, 6-
DTR override, D-1
escape code operations, 6-
load options, 3-3, 5-1, 5-2
local echo, 2- , 5-
result code display (quiet mode), 5- , D-
Result codes verbal/numeric, 5-
RS-232C DTE interface, B-1.1
Single/multiphone installation, E-4
Disconnecting (H, +++), 6-8, 6-9
reasons (S17, S20), 7- , B-5.4
DOC, xi, 6-
DTE, defined, 4-
speed select (&B), 4-
DSR override (&S), 4-10
DTR, Data Terminal Ready, B-1.1, B-3.1, D-1
dropping to force disconnect, 6-
Dumb mode (DIP switch 8), B-3.2
Duplex, Half/Full, 5-

Echo, local 2-5, 5-
ENQ character, HP installations, App. E-5
Error checking, A-
Error control, using, 3-1, 3-2, 4-3--4-4, 4-5, 6-1
ERROR message, 5-4
Escape code (+++), 6-
changing ASCII definition (S2), 6-8, B-5.1
to terminate analog loopback test, E-6.3
Extended result code set, 5- , App. E-2
Extensions
calling another, E-4.1
transferring calls to (!), 6-

Factory settings, 5- , App. B-4
Fallback, data rate
link negotiation, 3-3, 4-8--49, App. E-2
online, 1-2, 4-3, E-2.3, F-1
FCC certification, viii
Fixed/variable rates, 3- ,4- , 4-
Flow control, 3- , 4-
Frame transmission, A-
Full duplex, 5-

Guard tone (&G), 6-10

Half duplex, 5-
Hanging up (H, +++), 6-
reasons (S20), 7- , B-5.3
Help screens, list under "Commands"
Hewlett Packard installations, 2-2, 4-7, App. E-5
HST (High Speed Technology)
features, 1-1, Glossary
error control modes, 3-1, 4-3

Inactivity timeout (S19), 1- , 3- , B-5.4
Indicator lights, 2-4, App. B-2
Inquiry (I) options, 7-
Installation, 2-1--2-4
International calls, 6-10--6-11

Leased line installation, operations, E-4.1
LED indicators, 2-4, App. B-2
Line feed, ASCII definition (S4), B-5.1
Link interface
disconnect reasons (S17, S20), 7- , B-5.3
operations, 3- , 4- , A-1--A-3, App. E-2
speed select (&N), 4-
Load number, DOC, xi
Local echo, 2-5, 5-
Loopback, analog, App. E-6

Manual, how to use, xii
Memory, modem
nonvolatile randam access (NRAM), 3- , 5- , App. B-4
random access (RAM), 7- , Glossary
read only (ROM), 7- , Glossary
MNP, Microcom Networking Protocol, 1- , 4-1. App. A  (also see
ARQ)
Service levels, A-1--A-3
Modem
defaults, App. B-4, App. C
defined, Glossary
installation, 2-2--2-4
problems and solutions, App. D
repair, viii, D-3
Modulation, 1-1, F-
Multiphone installations (DIP switch 7), B-3.2, E-4.1

NO ANSWER result, 5- , 6-
NO CARRIER result, 5- , 6-
reason (S20), 4- , B-5.3
NO DIAL TONE result, 5- , E-1.1, E-4.1, E-6.1
Nonvolatile random access memory (NRAM)
configuring, 5- , App. B-4
defined, 5-
options, App. B-4
resetting to (Z), 5-
writing to (&W, &Zn=s), 5-

OK message, 2-5, 5-
Online local echo, 5-
Online fallback, 1-2, 4-3, E-2.3, F-1
Operations
auto answer, 6-
auto dial, 6-2--6-8
error control, 3-1, 4- , 6-
flow control, 3- , 4-
Originate mode, 2-6, 6- , E-1.1, E-4.1, E-6.1, E-6.2

Parity, 6-1
defined, Glossary
Party lines, ix
Pause during dial (,), 6-
Phone company, connecting to, ix
Phone line interface, 2-4, F-1
dedicated or short line, E-4.1
multiphone (DIP switch 7), B-3.2, E-4.1
PBX installations
DIP switch 7, B-3.2
procedures, E-4.1
Phone jacks
on Courier, 2-4
RJ11C (single phone), 2-1, B-3.2
RJ12, RJ13 (multiphone), B-3.2, E-4.1
Phone number storage (&Zn=s), 5-
Placing a call, 3- , 6-
Pound sign (#), 6-
Problems
and solutions, App. D
ARQ compatibility (S17), B-5.4
Programming rate switching, App. E-2
Pulse dialing, 6-

Quiet mode, 5- , D-1, D-2

Radio/television interference, x
RAM, random access memory, Glossary
Rate select commands
DTE rate (&B), 3-, 4-
link rate (&N), 3-, 4-
Rate switching, 3-2, 3-3, 4-8, App. E-2
Received data flow control (&I, &R), 4-
Redial/re-execute
continuous (A>), 6-
one time (A/), 6-
Remote echo, 5-
Repeat mode commands (>, A>), 6-
Requirements, operating, 2-1
9600 bps, 3-
MNP, 3-1
ventilation, 2-
Reset to NRAM defaults (Z), 5-
Response time, 1-
Result code sets, 5-
Retrain sequence, 1-2, 6- , App. E-3
Retransmission, 3- , 4- , A-
maximum to timeout, 4-
RING result code, 6-
RINGING result code, 5-
RJ11C jack, 2- , B-3.2
RJ12/RJ13 jack (multiphone line), B-3.2, E-4.1
RMA (Return Materials Authorization) number, viii, D-4
ROM, read only memory, 5- , 7-
defined, Glossary
RS-232C interface, App. B-1
CD (DIP switch 6), B-2.1, B-3.2, D-1, D-2
connectors, 2-1, 2-4
CTS (&H), 4-
DSR (&S), 5-
DTR (DIP switch 1), B-2.1, D-1
RTS (&R), 4-

Serial transmission, Glossary
Service levels, MNP, A-1--A-3
Settings
default, App. B-4, App. C
interface, Ch. 4
internal, Ch. 5
quick reference, Ch.3
Shorting A/A1, multiphone lines, B-3.2, E-4.1
Speaker (audio monitor), 5-
Speed recognition, 4-8, 6-1, App. E-2
Speed select
DTE rate (&B), 3-, 4-
link rate (&N), 3-, 4-
S-registers, 5- , 7-3, App. B-5
Standards
Courier compatibility with, 1-3, 6-1, F-1
RS-232C, App. B-1, B-3.2
Start/Stop bits, 6-1, F-1
Store phone number (&Zn), 3-3, 5-

Technical Specifications, App. F
Technical Support, USRobotics, viii, D-4
Telephone company, connecting to, ix
Television/radio interference, x
Terminal (DTE) interface speed select (&B), 3-, 4-
Terminal Mode, 2-4, Glossary
Terminology, 4- , Glossary
Testing, 2-5, App. E-6
Throughput, 1-1, 3-2, 4-8, A-2--A-3
Touch-tones
dialing, 6-
timing, spacing (S11), B-5.2
Transmission rate, 3-1, 3-2, 4-8, 6-1, App. E-2
DTE interface (&B), 3- , 4-
link interface (&N), 3- , 4-
Transmit data flow control (&H), 3-1, 3-2, 4-3, 4-5--4-6
Trellis coded modulation, 1-1, F-1
Turnaround, high speed channel, 1-1, 3-2--3-3, F-1

Unattended operation, 6-8
United Kingdom requirements
CCITT answer sequence (B), 6-10
Guard tone enalbed (&G), 6-10
Pulse dial make/break ratio (&P), 6-11

Variable/fixed data rates
DTE interface (&B), 3- , 4-
link interface (&N), 3- , 4-
Ventilation, 2-
Voice/data communications
configuring for, 2-4
using both, App. E-1

Warranty information, viii
Word length, 6-1, F-1

XMODEM-type protocols, 4-2, 4-5, B-5.3

YMODEM, 4-2, 4-5, B-5.3

ZMODEM, 4-2

end.