14
RS-232 TO FIBER OPTIC MULTIPLEXOR
This sampling and reconstruction induces variable propagation delays on
each signal, since signals coming into the mux from external sources will not
necessarily be synchronized to the internal sampling clock.
Maximum timing distortion is 13.2 µs, which is 1/4 of one bit time at the
maximum input data rate of 19.2 Kbps.
Total propagation delay of signals from the input of one multiplexor to the
corresponding output of the other multiplexor is 14 to 27 µs, plus 5 ns per
meter of fiberoptic cable. All of these time delays are the same for both the
8-channel unit and the 16-channel unit.
4.3.2 S
IGNAL
F
UNCTIONS
Functions of the multiplexor channel interface signals are described below.
All outputs except Data Set Ready and Data Carrier Detect go to the negative
(MARK or OFF) state if the optical signal is not being received from the other
multiplexor. Also, all inputs will appear to be a negative level if they are left
open.
Table 4-1 on page 16 shows all of the signals, their pins, directions, and
originating and receiving devices.
Data Set Ready (DSR, Pin 6)
All DSR outputs of all channels are connected in parallel to a common pull-
up resistor, and will be at the true level whenever the multiplexor is powered
ON.
Data Carrier Detect (DCD, Pin 8)
All DCD outputs of all channels are connected in parallel to a separate pull-
up resistor in the same fashion as the Data Set Ready output, and will also
always be true whenever the multiplexor is powered ON.
Transmit Data (TXD, Pin 2) and Receive Data (RXD, Pin 3)
The signal fed into the Transmit Data input (Pin 2) of the channel is
transmitted through the optical link and appears at the other multiplexor
channel as the Received Data output (Pin 3).
