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COURIER HIGH SPEED MODEMS
ANALOG LOOPBACK-&T1, &TB
&T1
This test checks the operation of the modem's transmitter and
receiver. Data flow is shown in Figure F-1.
Transmitter
Telco
Receiver
Figure F-1. Data Flow During Analog Loopback
There are two analog loopback options. The first, &Tl, involves
your typing data that you can verify at your screen.
The second option, &TS, 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: HST or Dual Standard modems must be tested at 2400
bps or lower to avoid asymmetrical modulation at higher speeds.
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 518 as a test timer, as explained earlier.
3.
Send the modem the following command.
AT &MO & 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 518, the modem automatically stops
the test at the timeout, exits AL mode and responds OK.
F-2
Modem Testing
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