V.34 Faxmodem (250-3037) Diagnostics Faxback Doc. # 14484
Your modem can run several advanced self tests. You use the &T command to
perform these tests. Under normal use, you should never need to use these
functions. But, you might be instructed to run one of these tests if you
have difficulty calling another modem.
In order to use the test commands, your modem must be in direct mode with
error correction and data compression disabled. To put the modem into
direct mode type &Q0. Your modem will respond with "OK". You are then
ready to use the test commands.
The following chart summarizes the available tests:
Command Function
&T0 Stops any test in progress.
&T1 Start Local Analog Loopback Test.
&T3 Remote Digital Loopback Test.
&T4 Enable Remote Digital Loopback Request.
&T5 Disable Remote Digital Loopback Request.
&T6 Request Remote Digital Loopback Test.
&T7 Request Remote Digital Loopback Test with automatic
test pattern generation/checking.
&T8 Local Analog Loopback Test with automatic test pattern
generation/checking.
TEST TIMER
Register S18 controls how many seconds any test runs. You can set this
register to any value from 0 to 255. If you set the value lo 0 (default),
your modem performs the test until you manually halt the test with the &T0
command.
To change the setting, enter AT S18=n <ENTER> where n=1-255.
&T0: Halt Test
AT &T0 <ENTER> halts any test in progress. If your modem is running a remote
test with another modem, or if it is running an analog loopback test, you
must first enter the escape code (+++) to enter the command mode. Examples
of using &T0 are included with each test.
&T1: Local Analog Loopback Test
The local analog loopback test is the first test you should run if you
think your modem is not operating correctly. This test checks your
computer's communications port and your modem. This does not send
information over the phone line, so you do not need to dial another
computer first.
To perform the test:
1. In your modem's command mode, type:
AT &T1 <ENTER>
2. Now type. Everything you type should appear on the screen exactly as
you enter it.
3. If you have not set the test timer, stop the test by typing: +++
Your modem responds with: OK
Then type: AT &T0 <ENTER>
Your modem again responds: OK
The test stops.
Otherwise, the test stops automatically after the timer elapses.
If what you typed appeared on the screen, you know that your modem and your
computer are communicating with each other properly.
If there is a problem:
1. Be sure you have not connected to a computer service. If necessary,
unplug the phone line.
2. If you do not see anything on your computer screen or if you see
incorrect characters when you type, be sure you have set your
communications software to the correct port (default COM 2) and speed
(1200 or 2400 bps).
3. If you still have problems see Faxback Doc. # 14478.
&T3: Remote Digital Loopback Test
This tests a remote modem. You use this test with modems that do not
themselves have a digital loopback test feature. This command makes your
modem loopback (echo) everything it receives from a remote modem. You must
be communicating with the other system when you start this test.
To run this test:
1. Escape to the command mode by typing +++.
2. To start the test, type:
AT&T3 <ENTER>
3. Now, everything the other computer sends loops back without ever
displaying on your computer's screen.
4. If you have not set the test timer, stop the test by typing:
AT&T0 <ENTER>
Otherwise, your modem stops the test automatically when the test timer
elapses.
Since this tests the remote modem, the person at that modem must determine
whether their modem is operating properly, and take appropriate action.
&T4: Enable Remote Digital Loopback
This commands your modem to respond to a request for a remote digital
loopback test (&T6 or &T7 from the other modem). This feature is enabled
by default, so you need only enter this command if you have disabled the
feature with the &T5 command.
With this feature enabled, your modem begins to loopback all information
sent to it from a remote modem, after that modem requests a digital
loopback test.
&T5: Disable Remote Digital Loopback
This commands your modem to ignore any request for a remote digital
loopback test.
&T6: Request Remote Digital Loopback
This commands your modem to request a remote digital loopback test from the
remote modem. You must be communicating with another system to use this
command, and the other system's modem must support remote digital loopback
tests and have its remote digital loopback test enabled (&T4).
Additionally, the communication speed of your modem must be set to 2400
bps. In order to do so, enter the following command string while in
direct mode AT&Q0537=6N0.
To perform this test:
1. Escape to the command mode by typing: +++
Your modem responds with: OK
2. To start the test, type: AT &T6 <ENTER>
If the remote modem does not support this test, or if the remote modem
has disabled, your modem responds with: ERROR
Otherwise, the test is underway.
3. Type anything. As you type, the characters are sent to the remote
modem, then they loop back to your system. So, everything you type
should appear on your computer.
4. If you have not set the test timer, stop the test by typing: +++
Your modem responds with: OK
Then, type: AT&T0 <ENTER>.
The test stops.
If what you typed appears on your screen exactly as you typed it, your
computer, your modem, the telephone line, and the remote modem are all
working properly.
If there is a problem:
1. Be sure you have dialed and connected to the remote system.
2. Pick up an extension phone and confirm that you can hear the tones
indicating a connection.
3. If the message does not come through, or if it comes back garbled, you
might be having telephone line problems. Or, you might not have your
communications program set to the correct speed.
4. If you cannot resolve the problem, see Faxback Doc. # 14478.
&T7: Request Remote Digital Loopback Test With Pattern Generation/Checking
This test is like the &T6 command, but your modem automatically generates
a test pattern and compares what it receives with what it sends, so you do
not have to type a test message. The communication speed of your modem
must be set to 2400 bps. In order lo do so, enter the following command
string while in direct mode AT&Q0537=6N0.
To run this test:
1. Connect to a remote system, then escape to the command mode by
typing: +++
Your modem responds with: OK
2. To start the test, type: AT &T7 <ENTER>
3. If you have not set the test timer, stop the test by typing: AT&T0
<ENTER>
Otherwise, wait for the test timer to expire. If everything is
operating correctly, your modem responds with: 000 OK
If your modem responds with a number other than 000, this indicates how
many errors your modem detected during the test. For example, 023
indicates your modem detected 23 errors. 255 indicates your modem
detected 255 or more errors.
It is normal to occasionally get errors. If the number of errors is
excessive, you might have connected through a noisy telephone line. If
the number of errors is consistently high with different systems, you
might have a problem with your modem.
&T8: Local Analog Loopback Test With Pattern Generation/checking
This commands your modem to test its internal functions. It automatically
loops information through itself, and keeps track of any errors. You
should not have dialed another system when you run this test.
To run the test:
1. In your modem's command mode, type: AT&T8 <ENTER>
2. If you have not set the test timer, stop the test by typing: AT&T0
<ENTER>
Otherwise, the test stops when the test timer expires. Your modem
responds with: 000 OK
If your modem responds with a number other than 000, this indicates how
many errors your modem detected during the test. For example, 023
indicates your modem detected 23 errors. 255 indicates your modem
detected 255 or more errors.
You might get occasional errors with this test, but they should not
occur consistently. If you receive many errors on more than one
occasion, see Troubleshooting (Faxback Doc. # 14478).
(ALL/tmc-04/08/95)