DataComm V.34 PL, Operation Manual

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Tests Digital Loopback
4-4 DataComm V.34 PL Modem 060R115-000
Installation and Operation Issue 1
Digital Loopback
The modem can be commanded to enter digital loopback, illustrated below, by means of the front
panel. This loopback is used while a call to the distant modem is established. In digital loopback,
the local received data is coupled to the transmitter input, so that the remote unit can perform a
loopback test without commanding remote loopback. In asynchronous mode the clocks are clamped
at the EIA interface.
Table 4-3 Digital Loopback
Step Front Panel
1. Establish data communications with a
remote modem.
2. To start the test, press DL.
3. The modem flashes the TM LED and
displays the test name (DL) while it is set-
ting up the test, then lights the TM LED and
decimal point one while the test is running.
4. Direct the remote attendant to enter data at
the remote DTE, then compare it with the
data that is looped back and displayed by
the DTE. If errors occur frequently, a
problem may exist in the local or remote
modems, the remote DTE, the remote
DTE-to-modem connection, or the
communication line. Refer to
Figure 4-1 ,
Fault Isolation Sequence.
5. To end the test, press AL, RDL or DL.
Modem
transmitter
DTE
Digital loopback
Modem
receiver
Communications line
V.34 PL
TR SD RD MR RS CS CO GD TM ALM OH
AL ST RDL DL SEL RST
ADV
1. Establish data communications with the remote modem.
2. To start the test. press DL.
3. TM flashes and the LCD displays the test name (DL) while it is setting up the test, then
TM lights and decimal point one is displayed while the test is running.
4. Ask the remote attendant to enter data at the remote DTE, then
compare it with the data that is looped back and displayed by the DTE.
5. To end the test, press DL.