Table of Contents
Advertisement
19.2-KBPS RS-232 LONG-HAUL MODEM (LHM-19.2)
6.1 Tests and Diagnostics
This section describes how the LHM-19.2's diagnostic tests work and explains how
to isolate faults. The LHM-19.2 has ITU V.54 compliant diagnostic capabilities for
performing local analog loopback and local and remote digital loopback. All three
of these loopbacks can be controlled with the LHM-19.2's front-panel pushbuttons.
If the LHM-19.2 is configured for it, the local analog and remote digital loopbacks
can also be controlled by toggling the signals on Pins 18 or 21 of the DTE
interface. The LHM-19.2 can perform a Bit Error Rate Test on the link using an
internal pseudo-random test pattern. Finally, the LHM-19.2 tests the line quality
continuously. For both the BERT and line-quality tests, the LHM-19.2 will use the
SQ LED and (optionally) the SQD signal to indicate the results.
Use the LHM-19.2's loop-test buttons (DIG, ANA, and REM) and LED indicators
to quickly check the modems, the attached devices, and the cables that
interconnect them. Before doing any of these tests, make sure that everything is
turned on and configured correctly. Also, if you're going to have a device attached
to either LHM-19.2 electronically trigger a loopback or perform a BERT, verify that
the device is operating well enough to be used for the purpose. If it isn't, either
have it repaired, swap in a working substitute, or attach a tester to the LHM-19.2
instead.
Loop tests are best performed in the order presented in Sections 6.1.2 through
6.1.4.
6.1.1 PATT B
UTTON
While the LHM-19.2 is operating, press its PATT button to start a Bit Error Rate
Test (BERT). This activates a circuit that (a) injects a bit pattern simulating
random data onto the transmit line and (b) compares this pattern against what
comes in on its receive line. (While this test is in progress, normal data
transmission is suspended.) The LHM-19.2's front-panel SQ LED (and—if SQD
signaling is enabled—its SQD output on Pin 21) will either be steadily ON (no
errors), flicker (intermittent errors), or dim or go OFF (for continuous errors).
BERT can be activated at a single LHM-19.2 during a local analog loopback test,
as shown in Figure 6-1 on the next page, or it can be activated simultaneously at
the two LHM-19.2s on either end of a communication link, as shown in Figure 6-2.
28
6. Troubleshooting
: B
E
R
IT
RROR
ATE
T
(BERT)
EST
Advertisement
Table of Contents
