Omron CQM1H-SCB41 operation manual Switches, Terminating Resistance Switch Wire or 4-Wire Switch

	Wiring	Section 2-1
Internal Circuits		The internal circuits for port 2 are shown below.

Pin 8: RDB (+)

Receiver

Terminating resistance: 200 Ω

Terminating resistance switch

Pin 6: RDA (–)

2-wire/4-wire switch

Pin 2: SDB (+)

Driver

Pin 1: SDA (–)

!Caution Confirm polarities before connecting RS-422A/485 cables. Some devices re- quire that SDA/B and RDA/B or signal polarities be reversed.

Applicable Connectors	Socket: XM2A-0901 (OMRON) or equivalent
	Hood: XM2S-0911-E (OMRON, conforms to ESD) or equivalent
	One Socket and one Hood are provided for each port.
Recommended Cables	CO-HC-ESV-3P 7/0.2 (Hirakawa Hewtech Corp.)
	Cable length: 500 m max.
	(The total combined cable length is 500 m max. T-branch lines must be a maxi-
	mum of 10 m long.)

2-1-4 Switches

Terminating Resistance Switch

2-Wire or 4-Wire Switch

The TERM and WIRE switches are on the front panel of the Serial Communica- tions Board. Refer to page 10 for a diagram of the Board.

When an RS-422/485 port is used, turn ON the switch if the Serial Communica- tions Board is on the end of the transmission line. Refer to information on specific serial communications modes for the ON/OFF settings.

Label	Name	Settings	Factory setting
TERM	Terminating	OFF: Terminating	OFF: Terminating
	resistance switch	resistance	resistance
		OFF	OFF
		ON: Terminating
		resistance ON

When an RS-422/485 port is used, set the switch to 2 when 2-wire connections are used, and set the switch to 4 when 4-wire connections are used.

Label	Name	Settings	Factory setting
WIRE	2-wire or 4-wire	2: 2-wire	2: 2-wire
	switch	4: 4-wire

Note Host Link, no-protocol, and 1:1 Data Link modes cannot use 2-wire RS-422A/485 communications. Always use 4-wire connections when using RS-422A/485 communications for these serial communications modes. Refer to 2-3 Wiring for connections.

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