18
RS-232 TO FIBER OPTIC MULTIPLEXOR
5.1 General
All circuitry of the multiplexor is on a single printed circuit board.
Troubleshooting by the user is limited to isolating a failure to either
one of the multiplexors or the fiberoptic cable.
5.2 Troubleshooting Procedure
1. If any failure occurs, first check for simple problems such as loose
connectors (especially the optical connectors), incorrect switch settings
(such as two internal-clock data rates selected on the same channel),
or blown fuses. The multiplexor has no logic that can “hang up” and
therefore no power-on-reset circuit is needed. All logic is self-clearing;
therefore, the common troubleshooting procedure of turning power
OFF and ON does not clear problems.
2. If a 3-to-1 adapter cable is used on a channel, check continuity of all
connections through that cable (see the pinning in
Section 4.3.3
).
3. Check for the possibility of interface incompatibilities between the
multiplexor and the particular terminal devices being used.
4. Verify that the proper protocol (synchronous or asynchronous) is selected
on the multiplexor and on each terminal device. If a problem mux
channel is operating in Mode 4 (sync, internal clock), verify that the
terminal device is set to receive the transmit clock from the mux rather
than to supply the transmit clock to the mux. If a problem mux channel is
operating in Mode 5 (sync, external clock), verify that the terminal device
is set to supply the transmit clock to the mux on the mux’s Pin 14.
5. If three asynchronous data-only channels are being fed into one channel
of the multiplexor, check for the possibility that the terminal device may
need the Data Set Ready, Data Carrier Detect, or Clear to Send signals,
none of which are normally provided in this mode. If the terminal device
does need one or more of these signals, the adapter cable may have to be
rewired (see
Section 4.3.3
).
5. Troubleshooting
