Fiber Optic Connections

receiver of the FOSTCDR must be connected together by tying terminal blocks (L) and (H) together and (G) and (K) together. This allows the FOSTCDR to communicate half-duplex over the same pair. Refer to Figure 1 for connection diagrams to your RS-422 or RS-485 equipment.

Figure 1: RS-422/485 Connection Diagrams

422/485 4W Device

FOSTCDR

485 2 Wire Device

FOSTCDR

TD A (-)

(K) RD A

Data

A (-)

(K) RD A

TD B (+)

(L) RD B

RD A (-)

(G) TD A

RD B (+)

GND

(H)TD B

(M)

Data B (+)

GND

(H)TD B

(M)

If termination is needed, the PCBD is laid out to allow a termination resistor (Rt) to be soldered in across the 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. Before making modifications to the FOSTCDR, be sure to consult B&B Electronics’ free RS-422/485 Application Note or other sources of information to see if termination is necessary. The Application Note is available from our Web site, or call and we will happily send you one at no charge.

The FOSTCDR uses a separate LED emitter and photo-detector operating at 820 nm wavelength. Connections to the emitter and detector are on ST type connectors. Most multi-mode glass fiber size can be used including 50/125 μm, 62.5/125 μm, 100/140 μm, and 200 μm. 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. A multi-drop ring configuration requires one fiber between TX and RX around the loop. See Figure 2 for typical point to point and multi-drop configurations.

2	FOSTCDR2999 Manual

B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104