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the identical pattern. When it receives the correct pattern, the
LED will turn off. If error insertion is on, the LED will blink once a
second if everything is operating properly.
TM
(Active Yellow) Solid Yellow indicates an Active Test Mode. The
unit may be placed in test mode by the local user or by the
remote user.
5.3 LOOP (V.54 & TELCO) DIAGNOSTICS
The Model 2701 offers three V.54 loop diagnostics. Use these diagnos-
tics to test the NTU and any communication links. These tests can be
activated via the front panel switches or via signals on the Model 2701/B
and C serial port interface.
Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local Model
2701, and is performed separately on each unit. Any data sent to the
local Model 2701 in this test mode will be echoed (returned) back 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 switch on the front panel in the “Local” position.
— Activate the “LL” signal on the DTE (2701/B and 2701/C only).
If you are not sure which lead is the “LL” signal, please refer to
Appendix D.