Because RS-422 and RS-485 signals are also available on the same
connector, take special care not to hook any external signals to these
pins. This is not a problem for most serial devices, but a custom cable
must be made that does not connect to the extra pins on the DB25
connector if your device has power or special non-standard outputs.
Figure 1. Fiber Point-to-Point & Multi-Drop Ring Diagrams
Power Jack
Product Overview
Fiber Optic
Inherent EMI/RFI &
Transient Immunity
FOSTC Specifications Table
Transmission
Dual multi-mode fiber optic cable
Point-to-point
Asynchronous, half- or full-duplex
Multi-drop
Asynchronous, half-duplex fiber ring
Serial Interface
RS-232, RS-422, RS-485
Power
Connection
2.5mm phone jack (tip positive)
or DB25 pins 25(+) and 12(-)
Temperature
-40 to 80 °C (-40 to 176 °F) operating
MTBF
570522 hours
Getting Started
1
The FOSTC provides the most versatile connection
possible between asynchronous serial equipment using
fiber optic cable. Applications include point-to-point
communications between serial devices or a multi-drop
fiber ring configuration allowing multiple serial devices to
communicate with each other.
It allows any two pieces of asynchronous serial equipment
to communicate full or half-duplex over two fibers at
typical distances up to 2.5 miles (4 km).
Fiber Optic -
ST Connectors
RS-232/422/485
DB25 Female
RS-232 Connections
3
RS-422 & RS-485 Connections
4
The RS-422/485 driver and receiver are connected to 4
pins on the DB25 connector. Signal ground is on Pin 7.
When connecting to a four-wire RS-422/485 device or
system, connect the output of your device to pins 16 (B or
+) and 17 (A or +). Connect the input to your device to pins
14 (B or +) and 15 (A or -).
For two-wire RS-485 systems, the driver and receiver
must be connected together by tying pins 14 and 16
together and 15 and 17 together. This allows the FOSTC
to communicate half-duplex over the same pair. See
Figure 3
for connection diagrams to your RS-422 or RS-
485 equipment.
If
termination
is needed, a spot on the PCBD of the
FOSTC labeled “Rt” allows you to solder a termination
resistor across RD(A) and RD(B) lines. Removing R8 and
R16 and replacing them with through-hole components
can also change the off-state bias resistor values.
RS-232 signals are pinned as a DCE device (input on Pin 2
and output on Pin 3).
•
A straight-through cable can be used from your DB25
port on any DTE device such as a PC or terminal.
•
A standard 9 to 25-pin adapter can be used in cases
where the serial port on the DTE device is a DB9.
•
A null modem cable or adapter that swaps pins 2 and 3 is
needed for connecting to modems or other DCE devices.
See
Figure 2
for connection diagrams to 9-pin and 25-pin
DTE and DCE devices.
Figure 2. RS-232 Connection Diagrams
Fiber Optic Connections
2
The FOSTC uses a separate LED emitter and photo-
detector operating at 820 nm wavelength. Connections to
the emitter and detector are on ST type connectors.
The FOSTC uses a separate LED emitter and photo-
detector operating at 820 nm wavelength. Connections to
the emitter and detector are on ST type connectors.
Almost any multimode glass fiber size can be used including
50/125
µ
m, 62.5/125
µ
m, 100/140
µ
m, and 200
µ
m. One
fiber is required for each connection between a transmitter
and receiver.
In a
point-to-point configuration
, two fibers are required
between the two modems - one for data in each direction.
In a
multi-drop ring configuration
, one fiber between TX
and RX around the loop is required.
