Multi-Tech Systems MultiModem USB MT5634ZBA-USB - Manual (Page 52)

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MultiModemUSB User Guide
5. To exit the test, type the escape sequence +++AT and press ENTER. This puts the modem
in online command mode. Then type either AT&T or ATH to return to command mode.
6. Your modem passes this test if the data received on your monitor are the same as the data
entered from your keyboard. If different data appear on your monitor, your modem is
probably causing the problem, though it could also be your computer. If your modem passes
this test, but you are receiving errors while on line, the remote modem or the phone line
could be at fault.
Remote Digital Loopback Test (V.54 Loop 2)
The remote digital loopback test tests the phone lines and the circuits of both your modem and a
remote modem. In this test, your modem must be on line with another modem that is set up to
respond to a request for remote digital loopback. (Note that some modems might not support remote
digital loopback or might have it disabled.) Data from your computer or terminal is transmitted through
your modem and over the phone line to the remote modem, where it is then looped back to your
modem.
AT&T6
OK
Computer or Terminal Local MultiModem Remote MultiModem Computer or Terminal
Digital Analog Digital Analog
AT&T6
OK
UUUUUUUUU
UUUUU
Figure C-2. Remote digital loopback test.
Test Procedure
1. Arrange to have &T6 set on the remote test modem.
2. Open your communications software and go into terminal mode. Type AT and press ENTER;
you should get an OK message. Type AT\N and press ENTER to disable error correction.
3. Dial the remote modem and establish your online connection.
4. Type the escape sequence +++AT and press ENTER to bring your modem into online
command mode.
5. Type AT&T6 and press ENTER. The local modem responds to this command by transmitting
an unscrambled marking signal, which causes the remote modem to place itself in digital
loopback mode. Then the local modem exits online command mode and enters data mode.
6. Enter data from your keyboard. For this test, typing multiple uppercase U characters is a
good way to send an alternating test pattern of binary ones and zeroes. Data received by the
remote modem enters its analog receiver, is converted to digital data, is reconverted into
analog, and then is transmitted back to your modem. Your modem passes this test if the data
received on your monitor is the same as the data entered from your keyboard.
7. To exit the test, type the escape sequence +++AT and press ENTER. This puts the modem
in online command mode. The modem should respond with an OK message. If you wish to
stay on line with the remote modem for normal data transmission, type AT&T and press
ENTER to exit the test, then type ATO and press ENTER to return on line. If you wish to
terminate the call, type ATH and press ENTER to hang up.