USRobotics V.34 user manual Figure H-1⎯Data Flow During Analog Loopback, AT &M0 &T1 Enter

COURIER HIGH SPEED MODEMS

ANALOG LOOPBACK⎯&T1, &T8

This test checks the operation of the modem's transmitter and receiver. Data flow is shown in Figure H-1.

Figure H-1⎯Data Flow During Analog Loopback

There are two analog loopback options. The first, &T1, involves your typing data that you can verify at your screen.

The second option, &T8, 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: Dual Standard modems must be set to B0 (default) or tested at 2400 bps or lower to avoid HST asymmetrical modulation at higher speeds.

&T1

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 S18 as a test timer, as explained earlier.

3.Send the modem the following command:

AT &M0 &T1 <Enter>

The modem disables error control, enters analog loopback (AL) mode, and sends a CONNECT message. The MR status light flashes.

H-2 Modem Testing