Patton electronic X.21 Interfaces - Manual (Page 15)

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5.3 LOCAL LOOP DIAGNOSTICS
The Model 2707 offers V.54 loop diagnostics. Use these diagnostics to
test the NTU and any communication links. This test can be activated
via DIP switches or via signals on the Model 2707 serial port interface.
Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local Model
2707, and is performed separately on each unit. Any data sent to the
local Model 2707 in this test mode will be echoed (returned) to the user
device (i.e., characters typed on the keyboard of a terminal will appear
on the terminal screen)
.
Figure 7. Local Loopback for a Network Termination Application
To perform a LL test, follow these steps:
1. Activate LL. This may be done in one of two ways:
– Place the DIP switch SW1-2 to the “ON” position.
– Activate the “LL” signal on the DTE (2707/C only). If you are not
sure which lead is the “LL” signal, please refer to Appendix C.
2. Verify that the data terminal equipment is operating properly and can
be used for a test.