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CHAPTER 5: Test Modes
5. Test Modes
Test configurations are set up by using the front-panel pushbuttons. These tests
should be performed when the unit is first installed or when a problem occurs.
The TST pushbutton enables the line driver’s transmitter circuitry and injects
marking data into the scrambled carrier bit pattern (after resetting the scrambling
circuitry). If the link is operating properly, the RD indicator on any unit receiving
this pattern will flash and then go off. This indicates the correct reception and
decoding of marking data.
The two loopback switches, DLB (digital loopback) and LLB (line loopback), loop
transmit data to receive data on the RS-232 interface. They also loop receive data
to transmit data on the RS-485 interface. The only difference between the two tests
is the circuitry of the line driver that is tested. See Figures 5-1 and 5-2 for an
illustration of these tests.
Figure 5-1. Line Loopback Test.
ENCODE
DECODE
PIN 2
PIN 3
RS-232
RX A, B
TX A, B
RS-485
LOCAL LOOPBACK
