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Tests
Digital Loopback
The modem can be commanded to enter digital loopback, illustrated in
commands. 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 6-3
Digital Loopback
Step
1.
Establish data communications with a remote modem.
2.
To start the test, type the escape sequence (
(enter). If modem responds with an error message, type:
AT&T3
mode, then re-enter the command.
3.
The modem flashes the TM LED while it is setting 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. For fault
isolation refer to
5.
To end the test, type:
HELLO
........
.......
Figure 6-4
6-6
AT Command Mode
Figure
6-1.
(enter) then type
AT&T0
TM LED on the modem front panel is lit during the test.
TX
LOGIC
DTE
INTER-
FACE
RX
LOGIC
Digital Loopback Data Path
SpectraComm Dual V.34 Modem
Installation and Operation
+++
) and, after the modem is in the command mode, type:
AT%T0
(enter) to go back on line.
ATO
TX
DRIVER
Communications
Line
ANALOG
RECEIVER
Digital Loopback
Figure
6-4, via AT
(enter), which resets the test
060R122-000
Issue 15
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