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C Loopback Tests
63
MultiModemZPX User Guide
Appendix C: Loopback Tests
Introduction
Each time you turn on your modem, it performs an automatic self-test to ensure
proper operation. Your modem also has three diagnostic tests: local analog loop-
back, remote digital loopback, and local digital loopback. These ITU-T V.54 loop-
back tests isolate telephone circuit and transmission problems.
In a loopback test, data from your computer loops through the circuits of your mo-
dem and/or a remote modem before it appears on your monitor. When the loop has
been completed, the data on your PC’s monitor should match the original data.
The local analog loopback test allows you to verify that the modem’s transmitter
and receiver circuits are functioning properly.
The remote digital loopback test allows you to verify that the local computer or ter-
minal, the serial ports, the local and remote modems, and the transmission line be-
tween them are functioning properly.
The local digital loopback test allows you to verify that the remote computer or ter-
minal, the serial ports, the local and remote modems, and the transmission line be-
tween them are functioning properly.
Local Analog Loopback Test (V.54 Loop 3)
In this test, data from your computer or terminal is sent to your modem’s transmit-
ter, converted into analog form, looped back to the modem’s receiver, converted into
digital form, and then sent to your monitor for verification. No connection to the
phone line is required.
Com
p
uter or Terminal
Digital Analog
AT&T1
CONNECT 9600
UUUUUUUUUUUU
Local MultiMode
m
Figure C-1. Local analog loopback test.
Test procedure
1. Using a communications program, set the baud rate to 9600 and go into terminal
mode.
2. Type AT&T1 and press ENTER. This places your modem in analog loopback
mode in the originate mode. A CONNECT message should appear on your dis-
play. The modem is now out of command mode and in a pseudo-online mode.