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1997-01-31
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STAC NOTE STAC NOTE
BASIC COMMUNICATIONS
(Applies to all ReachOut Modem versions through 5.X)
STAC FAX 8703 (05-25-1995)
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BACKGROUND
The problems below are symptomatic of basic communications
issues. They often involve a conflict with Interrupt Requests
(IRQÆs):
- Cannot open communications port.
- Communications port not available.
- Terminal Mode after dialing.
- Modem reported an error.
- Improper dialing or no dialing.
- Other Communications programs work, but ReachOut won't.
- Random disconnects (applies to ReachOut network product
also).
DISCUSSION:
Communications ports (Com Ports) have specific addresses that are
used to input/output information to/from the computer. Com Ports
also use IRQ's (interrupt request line) to interrupt what ever
the computer is doing to tell it about incoming information. Some
software uses this IRQ to detect that the Com Port has
information to be processed. Other software just watches the Com
Port address for information.
Each Com Port in the computer has a chip called a UART (Universal
Asynchronous Receiver Transmitter). The UART controls the flow of
information from the modem to the computer. Software that is
trying to talk to a specific Com Port will have a problem if
there are 2 UARTs responding to the same IRQ with different
messages.
PCÆs use a Com Port numbering scheme of Com1 to Com4. Depending
on the machines configuration it may have from 1 to 4 Com Ports
in it using the following addresses and IRQ's.
PORT ADDRESS IRQ
Com1 03F8 4
Com2 02F8 3
Com3 03E8 4
Com4 02E8 3
These are the standards within the industry, but can be changed
if the hardware and/or software allow it. Notice Com's 1 through
4 have unique addresses, but that Com1/Com3 share the same IRQ4
and Com2/Com4 share IRQ3. This effectively means you can't use
Com1/3 or Com2/4 devices at the same time since they share IRQ's
at all times. Some software will allow you to have a shared Com
Port as long as only one at a time is running in memory or
receiving information. ReachOut wonÆt allow a shared Com Port
because of speed.
For a modem to respond to ReachOut it must reside on its own Com
Port address and unique IRQ line. ReachOut will not look at a Com
Port that is shared with another piece of hardware/software on
the same Com Port or IRQ line.
SOLUTIONS
Finding your modem
Be sure your modem is plugged into your PC, via a serial cable,
or installed internally, and the telephone line is plugged into
the correct jack, usually marked "Line" or "Telco".
To test your modem configuration, use ReachOutÆs Modem
Diagnostics. The screen should produce a reset string, begging
with AT&F...., and an OK on the next line. If the OK is not
displayed, please follow the steps below. If an ERROR is
displayed, your modem is not accepting the reset string selected.
Close Modem Diagnostics, open Configuration/Setup, and select "A
Hayes Compatible 2400" modem. Repeat Modem Diagnostics. If an OK
is displayed, your ReachOut Data Speed can be raised to match
your UART CHIP (see below). A Hayes Compatible 2400 string may
not take advantage of your modemÆs error correction or data
compression. Using your modems manual, and ReachOut Modem Config,
you can write your own reset string. Use existing entries for
reference.
UART chips determine the speed at which data can be sent to your
modem. An 8250 UART can support a data speed of 19.2KBPS maximum.
A 16550 UART chip can support a data speed of 34.4 maximum. These
maximums are safe and reliable, and should be used when trouble
shooting. Data speeds higher then 34.4KBPS can be used when Com
Port Accelerator cards, or high speed internal modems are used.
Find your modem. The simplest way to locate your modem to go to a
DOS prompt and type:
ECHO ATH1>COM1
This command should take your modem off-hook, and sound a dial
tone. If the modem has lights, the OH light should be lit. To put
the modem back on-hook type
ECHO ATH0>COM1
Repeat this step for Com2, 3, and 4. Any errors reported, no dial
tone, no OH light, or returning to the command prompt, means that
the modem is not available on the Com Port. If the modem cannot
be found by this method, consult your manufacturer.
Note: this method will not work on Windows only modems.
Windows device drivers must be run to initialize the modem. A good
test for these modems is by using a Windows based terminal emulator.
The ECHO command will work there as well.
After locating your modem, use a diagnostic program, such MSD, to
verify its address and IRQ. In the case of MSD, select Q for IRQ
settings. The Com Port your modem is on must be on an IRQ to
itself, not sharing with any existing devices, such as other Com
Ports, network cards, etc.
If your modem is internal, and the ECHO method found the modem
on Com2, you may have an IRQ conflict. To prove this, run MSD,
and select Q for IRQ settings. Print Screen, or take note of the
Com Ports Detected. Power off the PC, remove your internal modem,
restart the system and run MSD again. Compare the Detected IRQ
versus the previous report. If Com2 is still detected, you have
an IRQ conflict. The modem must be set to another Com Port and
IRQ, or the existing device disabled. Consult you PCÆs
manufacturer for details on disabling Com Ports.
The suggested settings for devices and IRQÆs is;
Device IRQ
Com1 4
Com2 3
Internal Modem Com3 5
Network Card 10, 11, or 12
This Matrix will avoid IRQ conflicts.
Note: Network cards must also be set to unique IRQs.
With the above completed, use Windows Control Panel to set your
port. Select Ports, your modemÆs port, Settings, Advanced, and
verify the port Address and IRQ. This should be done for internal
modems with IRQ settings other than 3 or 4.
The last step is to set ReachOutÆs configuration to match the
settings of your modem
EXTERNAL MODEMS:
Com Ports that are built-in to most computers can be identified
by either a 9 pin or 25 pin connector on the back. Systems may
have both types of connectors indicating the computer has more
than one built-in Com Port. Connecting an external modem to
either type of connector works fine. If you are running MS-DOS 5
or later, to confirm which Com Port the modem is connected to,
turn on the modem and at any DOS prompt type "MSD" (MicroSoft
Diagnostics). Make sure neither Windows nor ReachOut are running.
Press "C" for Com Ports, look for a "Yes" in the CTS (clear to
send) field below the Com Port #'s. If there is a "Yes" in the
CTS field, the modem is connected to that Com Port. If you don't
see a "Yes" check your modem cable and modem to ensure a proper
connection.
When you find the modemÆs Com Port, check to make sure that its
"shared" port is listed as N/A. For shared ports, see the table
above. For example, if the modem is on Com 2, its shared port is
Com 4, and should be listed as N/A. If the shared Com Port has
entries in the fields, see the section NON-STANDARD IRQ SETUP.
The only other concern would be if any other non-communication
type board or device in the computer is set for the same IRQ that
the modem port uses (i.e. network boards, sound boards, emulation
boards).
INTERNAL MODEMS:
Before installing the modem, at any DOS prompt type "MSD", press
"C", note any Com Ports that state N/A under them. You must set
your internal modem for the first Com Port stating N/A in the
list. If the Com Port to be used "shares" an IRQ, change the IRQ
on the modem to any IRQ not in use by any other device in the
system. (i.e. network boards, sound boards, emulation boards).
Another way to check for the presence of Com Ports is to run MSD
and press "Q". The "Detected" column shows what Com Ports are
active. This report also shows what software is handling which
IRQ in the "Handled By" column. This allows you to determine what
IRQ's other boards are using (i.e. network cards, soundboards,
etc.).
NON-STANDARD IRQ SETUP
Most newer modems allow for non-standard Com Port settings (i.e.
Com3 IRQ5 ) to avoid any "sharing" of an IRQ. Some internal
modems do not allow for a non-standard settings (i.e. they will
only allow IRQ3 or IRQ4). For these modems you must disable one
of the internal Com Ports. This is usually done by moving a
jumper or switch on the board (consult your system
documentation.) Then set your internal modem for that Com Port.
Other modems list settings for Com5 through Com8. These are
actually Com1 through Com4 but on a different IRQ. Check the
modemÆs documentation or consult with the manufacturer.
ReachOut will only allow a setting up to IRQ 7, so you may have
to move one of your other devices to free up an IRQ for ReachOut.
Once the modem has been set, run ReachOut setup and change Com
Port to USER DEFINED and enter the address and IRQ #'s it is set
for. If you are going to be using Windows, run Windows - Control
Panel - Ports, select the port - Settings - Advanced, and set the
address and IRQ.
SOME STANDARD IRQ's AND THEIR USAGE:
IRQ DEVICE IRQ DEVICE
1 keyboard 2 2nd 8259
3 Com Ports 2/4 4 Com Ports 1/3 / some serial mice
5 LPT-2/some sound cards 6 floppy drives
7 LPT-1 8 system clock
9 redirected IRQ2 10 could be network cards, sound
cards, video
11 usually available 12 most bus mice / video capture
cards
13 math coprocessor 14 hard drive
OTHER INFORMATION:
Avoid skipping Com Ports. DOS sets up an "equipment" list on boot-
up, and it handles Com Ports by stacking them as Com 1 to 4 as it
finds them. This means that if you skip a port in your system
setup (i.e. only have devices set for Com1 and Com4), it will set
up the equipment list with Com1 as address 03F8, but it will set
the Com4 device as Com2 address 02E8
Windows may have some Comxbase=, Comxirq=, and Comxautoassign=
statements in its SYSTEM.INI file. Although some of these
statements may be required, removing the unused statements will
help. Remove all Comxautoassign= statements (where x= a number
from 1-4). Remove any Comxbase= and Comxirq= statements that
have the standard settings in them as listed on page 1 of this
document.
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Copyright 1995 Stac Electronics