3Com Courier, Reference

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Testing the Courier V.Everything Modem using AT&T n 15-3
Analogue Loopbac
Testing
Local loopback testing checks the operation of the Courier V.Everything
transmitter and receiver.
Using AT&T1
1
Send
AT&M0&N3S14.0=0
to prepare the modem for testing.
This command disables error control, fixes the connection rate at 2400
bps, and makes the modem return to command mode when you type
+++
.
2 Send
AT&T1
to the modem so it enters analogue loopback mode. If yo
are testing an external Courier V.Everything modem, the MR status light
flashes.
3 It will be looped back by your modem's transmitter for verification o
your screen
4 When the test is completed, send
+++
and then
AT&T0
to end the test.
Alternatively, you can end the test by sendin
ATH
, or
ATZ.
Be careful,
though, because ATZ resets the modem in addition to ending the test.
In either case, the modem responds with OK. If the modem sends an
ERROR message, you have issued an invalid command.
5 Send
AT&M4
, unless you used a reset command (ATZ).
If the Courier V.Everything modem is in online mode, still connected to a
remote modem, and you send AT&T1 or AT&T8, it drops the call, enters
analogue loopback mode, sends a CONNECT result, and waits for
loopback characters.
Stopping a Test
(AT&T0, ATS18)
To stop a test, send
AT&T0
to the modem, or set Register S18 to a
specified number of seconds (for example,
ATS18=10
). When the 1
seconds are up, the modem will stop the test automatically and return to
Command Mode. Send
ATH
to the modem to hang up, or send
ATZ
to
hang up and reset the modem to its defaults.