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Black Box Short Range Modem
Local Analog Loopback (LAL)
The Local Analog Loopback (LAL) test checks the operation of the local ME475A-R2
unit, and is performed separately on each unit. Any data sent to the local ME475A-R2
in this test mode will be echoed (returned) back to the user device. For example, char-
acters typed on the keyboard of a terminal will appear on the terminal screen. To per-
form a LAL test, follow these steps:
1. Activate LAL. This may be done in one of two ways: First, by moving the front
panel toggle switch DOWN to "Local". Second, by raising pin 18 on the RS-232
interface (Note: Make sure DIP switch S2-6 is OFF, and DIP switch S3-5 is ON).
Once LAL is activated, the ME475A-R2’s transmit output is connected to its own
receiver. The "test" LED should be lit.
2. Verify that the data terminal equipment is operating properly and can be used for
a test. If a fault is indicated, call a technician or replace the unit.
3. Perform a BER (bit error rate) test on each unit. If the BER test equipment indi-
cates no faults, but the data terminal indicates a fault, follow the manufacturer's
checkout procedures for the data terminal. Also, check the RS-232 interface
cable between the terminal and the ME475A-R2.
Remote Digital Loopback (RDL)
The Remote Digital Loopback (RDL) test checks the performance of both the local and
remote ME475A-R2s,
and
the communication link between them. Any characters sent
to the remote ME475A-R2 in this test mode will be returned back to the originating
device. For example, characters typed on the keyboard of the local terminal will appear
on the local terminal screen
after
having been passed to the remote ME475A-R2 and
looped back. To perform an RDL test, follow these steps:
1. Activate RDL. This may be done in two ways: First, by moving the front panel
toggle switch UP to "Remote". Second, by raising pin 21 on the RS-232 inter-
face.
Note
Make sure DIP switch S3-6 is ON; and DIP switch S2-6 is OFF.
2. Perform a BER (bit error rate) test on the system.
3. If the BER test equipment indicates a fault, and the Local Analog Loopback test
was successful for both ME475A-R2 units, you may have a problem with the
twisted pair line between the modems. You should then test the twisted pair line
for proper connections and continuity.
