20
RS-232 TO FIBER OPTIC MULTIPLEXOR
In addition to end-to-end tests with either BERTs or breakout boxes, local
or remote loopback tests can be performed using the procedures in
Sections
5.3.2 and 5.3.3
.
Other than the method of performing the actual loopback, the only
difference between loopback testing and end-to-end testing is that with
loopback tests, input fed into one multiplexor causes an output change at the
same multiplexor, rather than at the other end of the system (as in end-to-end
tests).
5.3.1 E
ND
-
TO
-E
ND
T
ESTING
To run an end-to-end test with standard BERTs, connect the testers to the
same-numbered channels at each end of the system. Configure the testers and
the channels for either internally clocked synchronous mode or asynchronous
mode and proceed as follows:
1. Verify that data can be transmitted from one tester to the other without
errors.
2. Verify that when Data Terminal Ready is turned ON and OFF at one end
of the system, Clear to Send at the other end of the system goes ON and
OFF. Note that Clear to Send is not affected by Request To Send unless a
gating adapter (refer to
Section 5.2
, Step 6) is used. If a gating adapter is
used, Clear to Send should be true at one end only if Request To Send is
true at that end and Data Terminal Ready is true at the other end.
3. If a channel of the multiplexor is operated in the triple asynchronous
mode with an adapter cable, set the testers for asynchronous data
transmission and connect them to the “A” female connector of the
adapter cable at both ends of the system and verify data transmission in
each direction. (Note that control signals are not provided to the tester or
accepted by the multiplexor.) After testing the “A” subchannel, repeat the
test for the “B” and “C” subchannels.
To test a channel of the multiplexor using RS-232 breakout boxes, set the
channel for internally clocked synchronous mode and verify, using either
the indicator LEDs on the breakout box or an oscilloscope, that the transmit
clock appearing at Pin 15 of the channel connector at one multiplexor also
appears at Pin 17 of the same channel of the other multiplexor. If possible,
