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Tests
Remote Digital Loopback with Self-Test
Remote Digital Loopback with Self-Test, illustrated in
can be commanded with AT commands. This command can only be entered after the call is
established and both ends are in the data mode. The test causes the local modem to generate a
pattern that is transmitted across the telephone line to the remote modem's receiver, looped through
to the remote modem's transmitter, and sent back across the telephone line to the local modem's
receiver for analysis. The pattern is made up of alternate ones and zeros for speeds of 1200 and
2400 bps. For all other speeds the modem generates a 511 test pattern. The number of errors is
displayed on the screen. The TM LED flashes to indicate detected errors. This test checks both
modems and the telephone line.
This test is not operational when the modems are passing data at 300 bps.
Note
This test cannot be performed if the remote modem is configured to ignore a remote digital loopback com-
mand.
Table 6-5
Remote Digital Loopback with Self-Test
Step
1.
Establish data communications with a remote modem.
2.
Check with the remote attendant that the remote modem accepts Remote Digital Loopback commands.
3.
To start the test, type the escape sequence (
(enter). If modem responds with an error message, type:
re-enter the command.
4.
The modem flashes the TM LED while it is setting up the test, then lights the TM LED while the test is
running. TM flashes each time an error is detected.
5.
If the timer, S-Register 18, is set to a value between 1 and 60, the test ends automatically after that value (in
10-second increments) is reached. The factory default for S-Register 18 is 000, meaning that the test will
continue indefinitely.
6.
To go back on line, type
TM LED is lit on the front panels of both modems; flashes for detected errors at the local modem.
PATTERN
GENERATOR
DTE
HELLO
INTER-
FACE
........
.......
ERROR
DETECTOR
Figure 6-6
6-8
AT Command Mode
) and, after the modem is in command mode, type:
+++
.
ATO
TX
TX
DRIVER
LOGIC
Communications
Line
RX
ANALOG
LOGIC
RECEIVER
local modem
Remote Digital Loopback with Self-Test Data Path
SpectraComm Dual V.34 Modem
Installation and Operation
Remote Digital Loopback with Self-Test
Figure
6-6, is controlled at the local end. It
AT%T0
(enter), which resets the test mode, then
RX
ANALOG
DTE
LOGIC
RECEIVER
INTER-
FACE
TX
TX
DRIVER
LOGIC
remote modem
AT&T7
HELLO
.......
........
060R122-000
Issue 15
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