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CHAPTER 5: Troubleshooting
6. There is a possibility of other problems with the Clear to Send signal.
Clear to Send at one end of the system is true only if Data Terminal Ready
is true at the other end of the system; therefore, problems might occur if
a terminal device that requires Clear to Send attempts to communicate
through the multiplexor with a terminal device that does not provide the
Data Terminal Ready signal. If this is the case, the Data Terminal Ready
signal can be provided by jumpering Data Set Ready (Pin 6) to Data
Terminal Ready (Pin 20) either at the terminal device or at the
multiplexor I/O connector.
It is also possible that a terminal device might become “confused” if the
Clear to Send output from the multiplexor to the terminal device is true
when the Request To Send output from the terminal device to the
multiplexor is false. (See
Section 4.3.3
for more information.) If this
problem occurs, although it is very rare, it can be solved with an adapter.
This adapter should consist of male and female RS-232 connectors with
all pins connected straight through except Pins 4 and 5 (Request To Send
and Clear to Send, respectively.) Between these pins is a gating circuit
that holds Clear to Send false when Request To Send is false. Consult us
for information on obtaining this type of adapter, if required. The best
source of information for determining if a terminal device is affected is
the terminal device’s manufacturer.
7. If all of the above possible problems have been eliminated or corrected,
and the multiplexors still do not pass data or seem to have data errors,
use the procedures in the following sections to isolate the source of the
problem.
5.3 Testing
Data transmission through the multiplexor can be tested by using the same
bit-error-rate testers (BERTs) used for testing standard RS-232 modems and
multiplexors. End-to-end tests using two testers are exactly the same as tests
with standard modems and multiplexors.
Since these multiplexors, like all fiberoptic modems and multiplexors, are
basically all-digital devices, a crude functional test can be performed with only
one or two RS-232 breakout boxes, and a fairly good test can be done with
breakout boxes and an oscilloscope.
