USRobotics V.34 user manual AT &M0 &T8 Enter, Figure H-2⎯Data Flow During Digital Loopback

COURIER HIGH SPEED MODEMS

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

H-4 Modem Testing