26
ASYNC/SYNC 2-WIRE SHORT-HAUL MODEMS
5.1.2 R
EMOTE
D
IGITAL
L
OOPBACK
Use this test to determine how the line-side circuits of the local and remote A/S2W
SHMs and the 2-wire line between them are performing:
1. Push the local unit’s REM (Remote Digital Loopback) pushbutton or (if the
unit’s RLB jumper is set to EN) raise the RL signal from the DTE to the unit.
The TEST LED should light on both units as the local unit sends a remote-
loopback command to the remote unit and the remote unit internally
connects its receiver input to its transmitter output (see Figure 5-2 below).
2. Perform a DTE test and/or BERT as described in Step 3 of the Local Analog
Loopback procedure. You can also press the local unit’s PATT button to have
it send a test pattern through the loop. (Press the PATT button again to stop
the test pattern.)
3. If Step 2 indicates a fault, but Local Analog Loopback testing was successful
for both A/S2W SHMs, either the line connection between the units is faulty,
or the 2-wire line circuits inside one or both of the units are not operating
properly. If possible, try a different line. If this is impossible, or if the problem
does not go away when you use a different line, call Black Box for technical
support.
4. After completing the test (or when the fault has been corrected), return the
REM button to the OFF position by pushing it again or, if you’re controlling
the test electronically, lower the RL signal from the DTE to the unit.
Proceed with the Local Digital Loopback test.
Fig. 5-2. Remote digital loopback.
LOCAL
DATA
TERMINAL
REMOTE
DATA
TERMINAL
RLB active
DATA
CLK
XMTR
XMTR
RCVR
RCVR
CLK
DATA
Summary of Contents for ME375A-R2
Page 33: ...NOTES...
