Mode Indicate/Mode Indicate Common (MI/MIC) closure is required by some
installations whose existing hardware does the dialing. The modems do
not Auto Dial.
In these situations, the modem must be forced off hook in Originate mode.
This is done by shorting (closing) two of the pins (not Tip and Ring) in
the phone connector. The modem is then ready to go online and accept data
when it connects with the number dialed by the system equipment.
Courier modems are shipped with MI/MIC disabled, that is, for normal use.
To set the modems for MI/MIC closure, you must do two things: physically
set jumpers on the modemÆs printed circuit board, and enable bit 5 of
Register S34 (ATS34=32 or ATS34.5=1). We recommend you then write that
setting to NVRAM as a power-on default.
Once you've set Register S34, have the system force the modem off hook
by closing the MI/MIC leads in the phone line connector. The modem's OH
(Off Hook) status light, or LED, goes on when the modem goes off hook.
***************************
SETTIING THE MI/MIC JUMPERS
You'll have to dismantle the modem case to set the two jumper switches on
the printed circuit board, as follows:
1. Power off the modem and disconnect all of its cables.
2. Turn the modem upside down. Remove the two square vinyl feet near
the back of the case, on either side of the bottom label's DIP switch
diagram. Be careful to put the vinyl feet aside, upside down, where
they won't become stuck to another object.
3. Remove the two Phillips screws located in the wells beneath the vinyl
feet.
4. Gently pry off the plastic volume slide-switch cover.
5. Raise the back end of the case bottom until it is at about a 60 degree
angle; lift it away from inside the front of the modem. Put the case
bottom aside.
6. Locate the voice/data switch at the front of the modem. Lift up and
remove the modem (printed circuit board), carefully easing the
voice/data switch out of its opening in the front panel.
7. Turn the modem rightside up and locate jumper switches J4 and J6,
8. The jumpers are black shunts that cover two out of three upright metal
contacts. As shown in the figure, set the jumpers so they cover the
two contacts on each switch that are closest to the front panel. The
third contact on each switch is exposed.
9. Replace the modem in the case top: ease the voice/data switch into
the opening in the front panel and make sure the back of the board
rests on the locator pins at the rear (from which you removed the
screws).
10. Connect the modem's RS-232, power and phone cables, in that order
(see Chapter 2). Be sure the phone cable is plugged into the jack
closest to the center of the modem--the jack represented by the wall
jack icon on the case bottom label.
CAUTION: When you power on the modem there will be potentially
hazardous voltage, particularly near the phone jacks. Do not touch
the board when the power is on.
11. Power on the modem. Try MI/MIC closure. Check to see that the Off
Hook (OH) status light goes on. If you dialed a number, listen for
an answer tone from the remote modem. Then drop the DTR signal. The
modem should go on hook and the OH status light should go off.
12. When you are sure the equipment is working correctly, disconnect the
modem's RS-232, power and phone cables, and replace the bottom of the
modem case. Ease the two nibs near the front corners into their
openings in the front of the case top, guide the rectangular slot
over the volume switch, and ease the back of the case bottom into
place. Replace the two screws, the two vinyl feet, and the volume
slide-switch cover.
***************
TROUBLESHOOTING
You may find that the modem does not respond to MI/MIC closure, which you
can monitor by observing the LED. Or the modem may fail to go back on hook
when the computer or terminal drops the Data Terminal Ready (DTR) signal.
The probable reason for either of these conditions is that your phone
equipment reverses MI/MIC polarity.
It's possible to solve this problem by reversing the modem's MI/MIC wiring.
You'll have to dismantle the modem case again and reset the two jumper
switches on the printed circuit board, as follows:
1. Lift off the jumpers from J4 and J6. Reverse the positions. That is,
on each switch, cover the center and rightmost contacts. Make sure
the jumpers cover two contacts on each switch, or you'll disable the
MI/MIC function.
2. Replace the modem in the case top: ease the voice/data switch into
the opening in the front panel and make sure the back of the board
rests on the locator pins at the rear (from which you removed the
screws).
3. Reconnect the modem's RS-232, power and phone cables, in that order.
Be sure the phone cable is plugged into the jack closest to the center
of the modem--the jack represented by the wall jack icon on the case
bottom label.
CAUTION: When you power on the modem there will be potentially
hazardous voltage, particularly near the phone jacks. Do not touch
the board when the power is on.
4. Power on the modem. Try MI/MIC closure again. Check to see that the
Off Hook (OH) status light goes on. If you dialed a number, listen for
an answer tone from the remote modem. Then drop the DTR signal. The
modem should go on hook and the OH status light should go off.
5. If closure is not working properly, review the steps in this section.
Be sure the jumper switches are in the correct positions. If you still
have problems, there may be a problem with the phone cable. Or there
may be a problem with your hardware.
6. When the equipment is working correctly, disconnect the modem's
RS-232, power and phone cables, and replace the bottom of the modem
case. Ease the two nibs near the front corners into their openings
in the front of the case top, guide the rectangular slot over the
volume switch, and ease the back of the case bottom into place.
Replace the two screws, the two vinyl feet, and the volume slide-switch
cover.
Appendix H--Modem Testing
Testing is available with the &T command or Register S16. All loopback
testing conforms to ITU-T Recommendation V.54. Earlier U.S. Robotics high
speed modems, however, did not perform the &T test repertoire.
Only one test can be performed at a given time. If you send a test
command while the modem is in test mode, you'll receive an ERROR message.
NOTE: Testing is not available when the modem is in synchronous mode:
&M1, &M6, &M7.
***************
Testing With &T
The tests supported through the &T command include analog loopback, digital
loopback and remote digital loopback. Users can key in their own data
during testing, or use the modem's internal test pattern and error detector.
In all cases, disable error control before testing. If the modem is
detecting errors and retransmitting the affected data, your results will
be invalid.
During testing, the MR status light flashes.
***********************
Ending a Test--&T0, S18
Issuing the &T0 command terminates a test. Alternatively, set Register
S18 to a specified number of seconds, for example, S18=10. When the 10
seconds are up, the modem automatically ends the test and returns to
Command mode. If the test was Analog Loopback, the &T0 command hangs up
the modem. If the test was Digital or Remote Digital Loopback, issue an
ATH command to hang up the modem, or an ATZ command to hang up the modem
and reset it to its defaults.
NOTE: If you use the S18 test timer, but in the process of testing you
issue an ATZ command, S18 resets to zero and the timer is disabled. You cannot store a value for S18 in nonvolatile memory; its power-on and reset default is always zero.
*************************
Analog Loopback--&T1, &T8
This test checks the operation of the modem's transmitter and receiver.
There are two analog loopback options. The first, &T1, involves your
typing data that you can verify at your screen.
The second option, &T8, is an internal self-test that does not involve
the keyboard or screen. It isolates the modem from the computer
interface to give you a more specific result.
NOTE: Dual Standard modems must be set to B0 (default) or tested at
2400 bps or lower to avoid HST asymmetrical modulation at higher speeds.
***
&T1
1. If you are testing an HST or Dual Standard modem, set your terminal or
software to 2400 bps.
2. The modem must be in Command mode. If you wish, set Register S18 as a
test timer, as explained earlier.
3. Send the modem the following command:
AT &M0 &T1 <Enter>
The modem disables error control, enters analog loopback (AL) mode, and
sends a CONNECT message. The MR status light flashes.
4. Type recognizable data so that you can verify it when it is looped back
to the screen.
5. End the test. If you set S18, the modem automatically stops the test
at the timeout, exits AL mode and responds OK.
If you didn't set Register S18, wait one second and type +++ to bring the
modem back to Command mode. If DIP switch 9 is OFF, the modem also
hangs up and ends the test.
If DIP switch 9 is ON, type AT&T0 to end the test. Or send either ATH
or the command that resets the modem, ATZ. The latter two commands end
the test and hang up the modem. The modem responds OK. If the modem
sends an ERROR message, you have issued an invalid command.
6. If there were no errors, reset the modem to &M4, for error control,
unless you've issued the ATZ reset command.
NOTE: If the modem is in online-command mode, that is, still connected
to a remote modem, and you send it an &T1 or &T8 command, it drops the
call, enters AL mode, sends a CONNECT result and waits for loopback
characters.
***
&T8
This AL option causes the modem to send an internal test pattern to its
transmitter and loop it back to the receiver. An internal error detector
counts any errors and, when the test is ended, sends the number of errors
or 000 (no errors) to the screen.
Since you don't type anything during this test, and the modem does not send
anything to the screen, this option verifies only the modem. If there are
no errors but your problem continues, it may be at the computer interface.
1. If you are testing an HST or Dual Standard modem, set your terminal
or software to 2400 bps.
2. The modem must be in Command mode. If you wish, set Register S18 as a
test timer, as explained earlier.
3. Send the modem the following command:
AT &M0 &T8 <Enter>
The modem disables error control and enters AL mode. The MR status
light flashes. The modem sends its internal test pattern to the
transmitter, and loops the pattern back to the receiver. You will
not see any data on your screen.
4. End the test. If you set S18, the modem automatically stops the test
at the timeout. If you didn't set Register S18, type AT&T0 to end the
test. Or use ATH or the command that resets the modem, ATZ. Both of
the latter end the test and hang up the modem.
The modem hangs up and returns a three-digit code, followed by OK. A
code of 000 indicates no errors were found. A code of 255 indicates
255 or more errors. An ERROR message indicates that you issued an
invalid command.
5. If there were no errors, reset the modem to &M4 for error control
unless you issued the ATZ command.
***
&T2
This option is reserved.
*********************
Digital Loopback--&T3
If your modem has passed the AL test, this test can help you locate
a problem with a remote modem or the telephone channel.
NOTE: This test requires the modem to establish a connection and return
to online-command mode in response to the +++ escape code. DIP switch 9
must be set ON so that the modem does not hang up on receipt of the escape
code. After you change the switch, issue ATZ to the modem to initiate
the new setting.
As with AL testing, HST and Dual Standard modems should be tested at
2400 bps or lower.
1. Set the modem to &M0, to disable error control. HST and Dual Standard
modems should be set to 2400 bps or lower to avoid asymmetrical
modulation at higher speeds. Establish a connection with the remote
modem.
2. Bring the modem back to Command mode with the +++ escape code. Then
send it the AT&T3 command. The modem enters DL mode and the MR
status light flashes.
3. The remote user should type a short message. It will be looped back
by your modem's transmitter for verification on the remote screen.
You will not see the message or any other data.
4. When the remote user has completed the test, issue the AT&T0 command
to end the test. Or send either ATH or the command that resets the
modem, ATZ. The latter two commands end the test and hang up the
modem. The modem responds OK. If the modem sends an ERROR message,
you have issued an invalid command.
5. Reset DIP switch 9 OFF if you normally use the factory default. Reset
the modem to &M4 unless you used the reset command, ATZ.
********
&T4, &T5
The &T4 option causes the modem to grant a remote modem's request for a
Remote Digital Loopback test.
The &T5 option cancels &T4, and the modem fails to recognize such a
request. This is the default so that your modem isn't subject to
another user calling and tying up your modem without your permission.
*********************************
Remote Digital Loopback--&T6, &T7
This test, like the local digital loopback test, verifies the condition of
both modems and the phone link.
The request for and granting of Remote Digital Loopback testing requires
that both modems use ITU-T V.22 standard signaling. The test must be
performed at 2400 bps or lower. If the remote modem does not have the
capability or is not set to respond (&T4), you will get an ERROR result
code.
As with Analog Loopback, there are two Remote Digital Loopback options.
If you select &T6, you send keyboard data to the modem and verify it
when it is returned over the phone lines and to your screen. If you
select &T7, the modem sends its internal test pattern and returns an
error count to your screen.
NOTE: Both test options require the modem to establish a connection and
return to online-command mode in response to the +++ escape code. DIP
switch 9 must be set ON so that the modem does not hang up on receipt
of the escape code. If necessary, set the switch ON and then issue the
ATZ command to the modem to initiate the new switch setting.
***
&T6
1. Set the software to 2400 bps or lower. Set the modem to &M0. If you
wish, set the S18 timer.
Establish a connection with the remote modem. If you haven't already
done so, arrange with the remote user to cooperate with your testing
and, if necessary, set the remote modem to acknowledge the RDL request.
For example, older U.S. Robotics high speed modems need to be set to
S16=8.
2. Bring the Modem back to Command mode with the +++ escape code. Send it
the AT&T6 command. The modem enters RDL mode and the MR status light
flashes.
3. Type a short message. It will be looped back to your modem by the
remote modem and to your screen for verification. (The remote user
will not see your data.)
4. End the test. If you set Register S18 the modem automatically ends the
test when the test timeout is reached. If you didn't set S18, type AT&T0
to end the test. Or send either ATH or the command that resets the modem,
ATZ. The latter two commands end the test and hang up the modem. The
modem responds OK. If you issue an invalid command, the modem sends an
ERROR message.
Data errors indicate a problem with the remote modem or the phone link.
If you have not performed analog loopback testing with your modem, the
problem may also lie with your modem.
5. Reset DIP switch 9 OFF unless you normally set that switch ON, and issue
ATZ to the modem to initiate the new setting. Reset the modem to &M4
unless you used the reset command, ATZ.
***
&T7
This test option causes the modem to send an internal test pattern through
the Remote Digital Loopback. An internal error detector counts any errors
and, when the test is ended, sends the number of errors or 000 (no errors)
to the screen.
You don't need to type anything during this test. The modem sends only
its final error count to your screen.
1. Set the software to 2400 bps or lower. Set the modem to &M0. If you
wish, set the S18 timer.
Establish a connection with the remote modem. If you haven't already
done so, arrange with the remote user to cooperate with your testing
and, if necessary, set the remote modem to acknowledge the RDL
request. For example, older U.S. Robotics high speed modems need to
be set to S16=8.
2. Bring the modem back to Command mode with the +++ escape code. Then
send it the AT&T7 command. The modem enters RDL mode and the MR
status light flashes.
The modem sends its internal test pattern to the remote modem, which
loops it back to your modem. You will not see the data on your screen.
3. End the test. If you set S18, the modem automatically stops the test
when the timer times out. If you didn't set Register S18, type AT&T0
to end the test. Or send either ATH or the command that resets the
modem, ATZ. The latter two commands end the test and hang up the modem.
The modem responds OK. If you issue an invalid command, the modem
sends an ERROR message.
When you terminate the test, the modem returns a three-digit code,
followed by OK. A code of 000 indicates no errors were found. A code
of 255 indicates 255 or more errors.
If you've performed an Analog Loopback and know your modem is working
properly, errors indicate a problem with either the phone connection
or the remote modem.
4. Reset DIP switch 9 OFF unless you normally operate with it ON. Issue
an ATZ command to initiate the new switch setting. Reset the modem to
&M4 unless you've sent it the ATZ reset command.
*************************
TESTING WITH REGISTER S16
Register S16 is a bit-mapped register with the following bit functions:
Bit Value Function
0 1 Analog Loopback (AL)
1 2 Dial Test
2 4 Test Pattern
3 8 Remote Digital Loopback (RDL)
NOTE: Earlier U.S. Robotics modems require bit 3 to be enabled in order
to grant RDL to a remote modem. The modem now requires its default &T4
setting instead. To perform RDL with a U.S. Robotics modem that does
not use the &T test repertoire, that modem should be set to S16=8 before
it can grant RDL testing.
****************************
Analog Loopback (AL)--S16=1D
As with the &T AL test, do not attempt this test under error control. HST
and Dual Standard modems should be tested at 2400 bps or lower, to avoid
asymmetrical modulation at higher speeds.
To use the modem's Test Pattern (S16, bit 2) instead of typing your own
data, see Test Pattern--S16=4 later in this appendix.
1. To initiate testing, type AT&M0S16=1D. The modem disables error control,
enters AL mode and sends a CONNECT result code. The MR status light
flashes.
2. Type data to the modem for the modem to transmit, loop to its receiver,
and output to the screen. An alternative is to use the Test Pattern,
described later.
3. End the test by not typing anything for one second, then typing three
pluses (+++), and waiting another second. This forces the modem back
to Command mode. If DIP switch 9 is OFF, the modem exits AL mode and
returns to Command mode. If DIP switch 9 is ON, the modem maintains
the connection when it receives the +++ escape code. Issue the ATH
command to end AL mode.
4. Reset the modem to Data mode, S16=0, and error control (&M4), or issue
the ATZ (reset) command.
****************
Dial Test--S16=2
The Dial Test is used for factory testing the frequencies of tone values.
When S-Register 16 is set to 2 and a single tone is dialed (e.g., ATD7
<Enter>), the modem continues to transmit that tone until you type another
Carriage Return.
*******************
Test Pattern--S16=4
The test pattern can be used instead of your typed data during Analog
Loopback (AL) or Remote Digital Loopback (RDL), using &T commands or S16.
The test pattern is available at all speeds. At 300 bps, the modem's
serial port rate must be fixed (&B1) and the link rate fixed at 300 bps
(&N1). At rates over 9600 bps, just set the modem for a fixed serial
port rate (&B1).
To use the test pattern during AL testing with S16, type the following
command. The test pattern is sent through the loopback.
AT&M0S16=5D
To use the test pattern during RDL testing with S16, type the following
command:
AT&M0S16=12
To use the test pattern with the &T AL or RDL tests, insert the test
pattern command, S16=4, before issuing the test command. The first of
the following commands initiates AL, the second RDL:
ATS16=4&T1
ATS16=4&T6
The test pattern alone (ATS16=4) is used for testing equipment and the
phone line. When S16 is set to 4, the modem transmits the test pattern
upon connection with a remote modem.
Ending Testing with the Test Pattern
Pressing any character key cancels all test pattern tests and hangs up the
modem. If you used Register S16, be sure to reset Register S16 to Data
mode when you reset the modem to its error control defaults, for example,
ATZ or AT&M4S16=0.
******************************
Remote Digital Loopback--S16=8
Responding Modem
The responding modem must be ready to act on the Courier's RDL request.
U.S. Robotics high speed modems should be set to &T4. If they do not
have &T testing capability, they should be set to S16=8.
Initiating Modem
1. If DIP switch 9 is OFF, set it ON so that it does not hang up on
receipt of the +++ escape code. Issue an ATZ command to initiate the
new switch setting.
2. Set the software to 2400 or 1200 bps. The ITU-T-specified RDL signals
are defined only for connections at 2400 or 1200 bps.
3. Disable error control by setting the modem to &M0. Then establish a
connection with the remote modem.
4. Bring the modem back to Command mode by sending it the escape code:
one second of no data, three pluses (+++), and another second of no
data.
5. When the OK result code appears, send the modem the following command:
ATS16=8 O
The modem enters RDL mode (S16=8), the MR status light flashes, and the
modem goes back online (O command). Then it transmits the ITU-T-defined
RDL signals, causing the remote modem to enter RDL mode.
6. Type any data at the keyboard. (Or send the test pattern.)
7. To end the test, send the modem the +++ escape code again to bring it
back to Command mode.
8. When the modem sends the OK result, reset the modem to Data mode with
the following command:
ATS16=0
The modem signals the responding modem that RDL testing is over.
Terminate the call as you normally would, and reset the modem to its
normal error control setting, &M4 or &M5.
Or, if you wish to resume data transmission with the remote modem, add
the O command to the ATS16=0 string to return the modem online. Keep in
mind, however, that error control is disabled. Because error control
is negotiated during the connection sequence, its status cannot be
changed until the modem is back on hook and in Command mode.
Appendix I--Software Upgrades
The Courier V.34 modem is software upgradable. You can download upgrades
from the USR Bulletin Board Service (BBS) to obtain maintenance fixes or
new features.
We suggest you retain a copy of the most recent upgrade on disk so you can
download it to your modem again, should the modem lose its code for any
reason.
The software download program requires DOS version 3.0 or higher and may
be run from the DOS shell under Microsoft Windows.
****************
Call the USR BBS
1. Call the USR BBS:
ATDT 708 982 5092 <Enter>
2. Unless you are running an ASCII-based communications program, answer
YES at the graphics prompt when you connect to the BBS.
3. Press Enter with each prompt until you come to the main menu.
*************************
Download the Upgrade File
1. At the command line of the main menu, type F (File) and press Enter.
Select area 5 (Courier) from the file area menu The most recent
zipped files will display.
2. Use the Enter key to scroll through the list and use the spacebar key
to highlight a file.
Scroll through the list and highlight the file named USRSDL.EXE.
Press Enter when it is highlighted to flag the file for download.
3. Press Enter to go back to the main menu.
4. At the command line on the main menu, type D and press Enter to
initiate a download.
5. Answer the download prompts according to your system requirements.
The file will be downloaded to the directory specified in your
communications software.
6. When the file transfer is complete and you are ready to leave the
BBS, type G (Goodbye) from the main menu.
******************
Upgrade your Modem
NOTE: Your modem must be turned on for the following operation.
1. At the DOS prompt of the directory where your copy of the file has been
downloaded, type USRSDL and press Enter. The zipped file will
self-extract several files onto your computer hard disk.
2. Type SDL and press Enter.
The .EXE file checks the code embedded in itself. If there is a problem,
an error message appears and the operation is terminated. If you receive
an error message, download the file again.
3. A screen appears with default COM port information.
If you want to alter the defaults, use the guidelines below.
/c=n Enter this command to select one of four predefined COM ports
on an IBM-compatible PC. Valid entries for n are 1, 2, 3, and 4.
The default is COM 2. If you change the COM port setting, a
compatible IRQ will be displayed.
/i=n Enter this command to set up a custom port. It specifies which
IRQ (interrupt request) the COM port will use to interrupt the
processor for service. Valid entries for n are 2, 3, 4, 5, and 7.
The default is IRQ 3.
/a=n Enter this command to specify a port address, where n is the
hexadecimal address of a custom port only.
/b=n Enter this command to specify the bit rate at which the COM
port will communicate with the modem. Valid entries for n are
9600, 19200, 38400, 57600, and 115200. The default is 57600 bps.
/q This command allows you to shut off most of the screen display
as the program upgrades your modem code for batch-mode execution.
You will not be prompted to accept settings.
/? This command displays a help screen.
4. A prompt asks if you want to "Download Using These Settings? (Y/N)."
Type Y if you want to continue. Type N if you want to abort the
operation.
NOTE: This is the only opportunity you will have to abort the operation.
5. Once you have accepted the settings, the software download will begin.
During this operation, the Modem Ready (MR) LED goes out.
6. When the operation has successfully completed, the "Modem reports
download successful" message displays and the MR LED lights up again.
***************
Troubleshooting
If your modem indicates an error, try running the SDL program at a lower
serial port rate. If your computer doesnÆt have a 16550 UART, a slower
serial port rate can make all the difference.
You can also try running the program on a different PC. An idiosyncracy
of an off-brand PC or an uncommon version of DOS my hang up the SDL program.
Appendix J--Glossary
Adaptive Speed Leveling (ASL)
Courier V.32 bis and V.32 terbo modems detect improved line conditions
and shift upward again to the next higher speed. The modems at both
ends of the connection adapt independently, each detecting and adjusting
to line conditions. ASL keeps the modems online, always operating at
the highest possible speed, and constantly ensuring data integrity.
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.
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 predefined 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.
Application (application program)
A computer program designed to perform a specific function, such as
a word processor or a spreadsheet.
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, MNP, and V.42.
ASCII
American Standard Code for Information Interchange. A 7-bit binary code
(0's, 1's) used to represent letters, numbers, and special characters
such as $, !, and /. Supported by almost every computer and terminal
manufacturer.
Asymmetrical Modulation
A duplex transmission technique which splits the communications channel
into one high speed channel and one slower channel. During a call under
asymmetrical modulation, the modem with the greatest amount of data to
transmit is allocated the high speed channel. The modem with less data
is allocated the slow, or back channel (450 bps). The modems dynamically
reverse the channels during a call if the volume of data transfer changes.
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.
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.
Bisync
Binary Synchronous Control. An earlier protocol developed by IBM for
software applications and communicating devices operating in synchronous
environments. The protocol defines operations at the link level of
communications, for example, the format of data frames exchanged between
modems over a phone line. See Protocol, HDLC, SDLC.
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 300, 1200, 2400, 4800, 9600, and 14400.
BPS
The bits (binary digits) per second rate.
Buffer
A memory area used as temporary storage during input and output
operations. An example is the modem's command buffer. Another is the
Transmit Data flow control buffer used for flow control and to store
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), or have some other value meaningful to the computer. In
user documentation, the term usually refers to 8-bit units or characters.
1 kilobyte (K) is equal to 1,024 bytes or characters; 64K indicates
65,536 bytes or characters.
Call Indicate
A call originating tone defined by ITU-T recommendation V.8.
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.
CCITT
Formerly, an international organization that defined standards for
telegraphic and telephone equipment. It has been incorporated into
its parent organization, International Telecommunication Union (ITU).
Telecommunication standards are now covered under Telecommunications
Standards Sector (TSS). ITU-T replaces CCITT. For example, the
Bell 212A standard for 1200 bps communication in North America was
referred to as CCITT V.22. It is now referred to as ITU-T V.22.
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, employ advanced techniques such as longer
transmission frames and data compression to increase cps.
Class 1/EIA-578
An American standard used between facsimile application programs and
facsimile modems for sending and receiving Class 1 faxes.
Class 2.0/EIA-592
An American standard used between facsimile application programs and
facsimile modems for sending and receiving Class 2.0 faxes.
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 U.S.
Robotics high speed modems, 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
When the transmitting modem detects redundant units of data, it recodes
them into shorter units of fewer bits. The receiving modem then
decompresses the redundant data units before passing them to the
receiving computer.
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.
Data Mode
The mode in which the fax modem is capable of sending and receiving
data files. A standard modem without fax capabilities is always in
Data mode.
DCE
Data Communication (or Circuit-Terminating) Equipment. In this manual,
the term applies to 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. The
communications channel may also be referred to as nonswitched because
calls do not go through telephone company switching equipment.
Default
Any setting assumed, at startup or reset, by the computer's software
and attached devices, and operational until changed by the user.
Digital Loopback
A test that checks the modem's RS-232 interface and the cable that
connects the terminal or computer and the modem. The modem receives
data (in the form of digital signals) from the computer or terminal,
and immediately returns the data to the screen for verification.
Digital Signals
Discrete, uniform signals. In this manual, the term refers to the
binary digits 0 and 1.
Duplex
Indicates a communications channel capable of carrying signals in both
directions. See Half Duplex, Full Duplex.
EIA
Electronic Industries Association, which defines electronic standards in
the U.S.
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.
U.S. Robotics high speed modems use adaptive equalization.
Error Control
Various techniques which check the reliability of characters (parity) or
blocks of data. V.42, MNP and HST error control protocols use error
detection (CRC) and retransmission of errored frames (ARQ).
Facsimile
A method for transmitting the image on a printed page from one point to
another. Commonly referred to as Fax.
Fax Mode
The mode in which the fax modem is capable of sending and receiving files
in a facsimile format.
Flash ROM
Read Only Memory that can be erased and reprogrammed.
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 indicators.
Full Duplex
Signal flow in both directions at the same time. In microcomputer
communications, may refer to the suppression of the online Local 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.
HDLC
High Level Data Link Control. A standard protocol developed by the
International Standards Organization for software applications and
communicating devices operating in synchronous environments. The
protocol defines operations at the link level of communications,
for example, the format of data frames exchanged between modems over
a phone line. See Bisync, Protocol, SDLC.
HST
High Speed Technology, U.S. Robotics' proprietary signaling scheme,
design and error control protocol for high-speed modems. HST
incorporates trellis-coded modulation, for greater immunity from
variable phone line conditions, and asymmetrical modulation for more
efficient use of the phone channel at speeds of 4800 bps and above. HST
also incorporates MNP-compatible error control procedures adapted to
asymmetrical modulation.
Hz
Hertz, a frequency measurement unit used internationally to indicate
one cycle per second.
ITU-T
International Telecommunication Union-Telecommunication sector.
Formerly referred to as 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 ITU-T V.22. For 2400 bps communication,
most U.S. manufacturers observe V.22 bis.
LAPM
Link Access Procedure for Modems, an error control protocol incorporated
in ITU-T Recommendation V.42. Like the MNP and HST protocols, LAPM
uses cyclic redundancy checking (CRC) and retransmission of corrupted
data (ARQ) to ensure data reliability.
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.
MI/MIC
Mode Indicate/Mode Indicate Common, also called Forced or Manual
Originate. Provided for installations where other equipment, rather
than the modem, does the dialing. In such installations, the modem
operates in Dumb mode (no Auto Dial capability), yet must go off
hook in Originate mode to connect with answering modems. See MI/MIC
Closure in Appendix G.
MNP
Microcom Networking Protocol, an asynchronous error control protocol
developed by Microcom, Inc. and now in the public domain. The protocol
ensures error-free transmission through error detection (CRC) and
retransmission of errored frames. U.S. Robotics modems use MNP
Levels 1-4 and Level 5 data compression. MNP Levels 1-4 have been
incorporated into ITU-T Recommendation V.42. Compare HST.
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 the analog 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.
Nonvolatile Memory (NVRAM)
User-programmable random access memory whose data is retained when
modem power is turned off. Used in Courier modems 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).
Online Fallback
A feature that allows high speed error-control modems to monitor line
quality and fall back to the next lower speed if line quality degrades.
The modems fall forward as line quality improves.
Originate Mode
A state in which the modem transmits at the predefined 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-type protocols
and the ARQ protocol implemented in Courier modems.
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 1's 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
correction are some of the operations that may be defined in protocols.
RAM
Random Access Memory. Memory that is available for use when the modem
is turned on, but that clears of all information when the power is
turned off. The modem's RAM holds the current operational settings,
a flow control buffer, and a command buffer.
Remote Access
A feature that allows a remotely-located user to view the Courier's
configuration screens and change the Courier's configuration. Password
protection is available.
Remote Digital Loopback
A test that checks the phone link and a remote modem's transmitter and
receiver. Data entered from the keyboard is transmitted from the
initiating modem, received by the remote modem's receiver, looped
through its transmitter, and returned to the local screen for
verification.
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's factory settings are stored in ROM and can be read (loaded)
into RAM as an operational configuration if DIP switch S10 is ON at
power on.
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.
SDLC
Synchronous Data Link Control. A protocol developed by IBM for software
applications and communicating devices operating in IBM's Systems
Network Architecture (SNA). The protocol defines operations at the
link level of communications, for example, the format of data frames
exchanged between modems over a phone line. See Bisync, Protocol, HDLC.
Synchronous Transmission
A form of transmission in which blocks of data are sent at strictly
timed intervals. Because the timing is uniform, no Start or Stop
bits are required. Compare Asynchronous Transmission.
Some mainframes only support synchronous communications unless their
owners have installed a synchronous adapter and appropriate software.
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.17
An ITU-T standard for facsimile operations that specifies modulation
at 14.4K bps, with fallback to 12K bps.
V.21--Fax
An ITU-T standard for facsimile operations at 300 bps. U.S. Robotics
or compatible fax devices then transmit or receive at higher speeds.
V.21--Modem
An ITU-T standard for modem communications at 300 bps. Modems made in
the U.S. or Canada follow the Bell 103 standard. However, the modem
can be set to answer V.21 calls from overseas.
V.22
A ITU-T standard for modem communications at 1200 bps, compatible with
the Bell 212A standard observed in the U.S. and Canada.
V.22 bis
An ITU-T standard for modem communications at 2400 bps. The standard
includes an automatic link negotiation fallback to 1200 bps and
compatibility with Bell 212A/V.22 modems.
V.23
An ITU-T standard for modem communications at 1200 bps with a 75 bps
back channel. Used in the U.K.
V.25
An ITU-T standard for modem communications. Among other things, V.25
specifies an answer tone different from the Bell answer tone. All U.S.
Robotics modems can be set with the B0 command so that they use the
V.25 2100 Hz tone when answering overseas calls.
V.25 bis
An ITU-T standard for synchronous communications between the mainframe
or host and the modem using the HDLC or character-oriented protocol.
Modulation depends on the serial port rate and setting of the
transmitting clock source, &X.
V.27 ter
An ITU-T standard for facsimile operations that specifies modulation
at 4800 bps, with fallback to 2400 bps.
V.29
An ITU-T standard for facsimile operations that specifies modulation
at 9600 bps, with fallback to 7200 bps.
V.32
An ITU-T standard for modem communications at 9600 bps and 4800 bps.
V.32 modems fall back to 4800 bps when line quality is impaired, and
fall forward again to 9600 bps when line quality improves.
V.32 bis
An ITU-T standard that extends the V.32 connection range: 4800, 7200,
9600, 12K and 14.4K bps. V.32 bis modems fall back to the next lower
speed when line quality is impaired, and fall back further as necessary.
They fall forward to the next higher speed when line quality improves.
V.32 terbo
Modulation scheme that extends the V.32 connection range: 4800, 7200,
9600, 12K, 14.4K, 16.8K, 19.2K, and 21.6K bps. V.32 terbo modems fall
back to the next lower speed when line quality is impaired, and fall
back further as necessary. They fall forward to the next higher speed
when line quality improves.
V.34
An ITU-T standard that allows data rates as high as 28.8K bps.
V.42
An ITU-T standard for modem communications that defines a two-stage
process of detection for LAPM error control.
V.42 bis
An extension of ITU-T V.42 that defines a specific data compression
scheme for use with V.42 error control.
V.8
ITU-T recommendation that defines procedures for starting and ending
sessions of data transmission.
V.Fast Class (V.FC)
Proprietary modulation scheme developed by Rockwell International for
data communication speeds up to 28.8K bps.
Word Length
The number of bits in a data character without parity, start or stop
bits.
Xmodem
The first of a family of error control software protocols used to
transfer files between modems. These protocols are in the public
domain and are available from many bulletin board services.
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.
Appendix K--Tecnical Specifications
Your modem uses multiple standard modulation protocols and is also
