RS-485 termination and biasing - OPT100

There are two banks of DIP switches on the underside of the RS-485 repeater. Switches for configuring the RS-485 output are at the front of the repeater, next to the grounding terminal (green screw).

1

DIP switches for configuring the RS-485 output.

2

DIP switches for configuring the internal serial connection. Do not change the settings of this bank.

Table 1. DIP switch configuration of RS-485 output

Switch number				Result
Switch 1	Switch 2	Switch 3	Switch 4	Communication mode
ON	ON	ON	ON	RS-485 2-wire half-duplex (default)
ON	OFF	OFF	OFF	RS-485 4-wire full-duplex
OFF	OFF	OFF	OFF	RS-422 full-duplex
Switch 5				Termination resistor
ON				Use built-in 120 Ω termination
OFF				Use external or no termination (default)
Switch 6				Transmit bias resistor
ON				Use external or no bias resistor
OFF				Use built-in 1.2 kΩ transmit bias resistor (default)
Switch 7				Receive bias resistor
ON				Use external or no bias resistor (default)
OFF				Use built-in 1.2 kΩ receive bias resistor

Switch 8 is not used.