B&B Electronics FOSTCDR manual Dip-Switch Setup, Point to Point

The most important consideration in planning the fiber optic link is the “power budget” of the fiber modem. This value represents the amount of loss in dB that can be present in the link between the two modems before the units fail to perform properly. This value includes line attenuation as well as connector loss. For the FOSTCDR the typical connector to connector power budget is 12.1 dB. Because 62.5/125 μm cable typically has a line attenuation of 3 dB per Km at 820 nm, the 12.1 dB power budget translates into 2.5 miles. This assumes no extra connectors or splices in the link. Each extra connection would typically add 0.5 dB of loss, reducing the possible distance by 166 m (547 ft.). The actual loss should be measured before assuming distances.

Figure 2: Typical Setups

		Point to Point
RS-232
RS-422	TX
			Duplex

RX

RS-232 RS-422

or RS-485	FOSTCDR		Multimode
Device	SW1:6 = OFF	RX	Fiber
or System

TX

FOSTCDR SW1:6 = OFF

or RS-485

Device or System

Full Duplex		TX
RS-232
RS-422	FOSTCDR
or RS-485	SW1:6 = OFF	RX
Device
or System
	MASTER

Multi-Drop Ring

Multimode

Fiber

Dip-Switch Setup

SLAVE

TX	RX
SW1:6 = ON	FOSTCDR

RS-232

RS-422

or RS-485 Device

or System

SLAVE

TX	RX
SW1:6 = ON	FOSTCDR

RS-232

RS-422

or RS-485 Device

or System

SLAVE

TX	RX
SW1:6 = ON	FOSTCDR

RS-232

RS-422

or RS-485 Device

or System

The Dip-Switch (SW1) on the FOSTCDR defines the mode of operation when being used for RS-422 or RS-485. Positions 1 through 5 on the switch determine the timeout of the RS-485 driver. Because the driver is controlled by hardware, a specific time must be set to tell the hardware how long to wait for data on the fiber side before turning off the RS-422/485 driver. If this time is set too short,

FOSTCDR2999 Manual 3

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