COURIER HIGH SPEED MODEMS
H-4 Modem Testing
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. Figure H-2 shows the data flow during DL testing.
Figure H-2
Data Flow During Digital Loopback