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Diagnostics
Local Loopback Test
The Local Loopback test isolates the DSU from the network by connecting the transmit logic
circuits to the receive logic circuits. The loopback provides a path through the DSU for an externally
generated test signal. The figure below demonstrates the Local loopback data path.
Figure 4-1
Test Procedure
1. Enter test data at the DTE.
2. Compare data entered at the DTE with data looped back and displayed by the DTE.
3. During Local Loopback:
•
TM LED illuminates steady ON during the test.
•
The DTE interface remains active.
•
The DSU loops transmit data from the DTE back as receive data.
•
Either the DTE or a bit error rate tester (BERT) connected to the DTE interface can
supply and check a test signal.
•
The device supplying the test signal is responsible for error detection and reporting.
4-2
DTE
DTE
INTERFACE
Local Loopback Test Data Path
SpectraComm 800 T3 Data Service Unit
Installation and Operation Manual
Diagnostics Overview
SC800 T3 DSU
Tx DRIVER
F
R
A
M
E
R
ANALOG
RECEIVER
T
3
N
E
T
W
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R
K
076R160-000
Issue 4
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