Omron NT31 NT31C manual 129

Connecting to the Host’s RS-422A/485 Port		Section 5-2
	Pin Nos. 9 and 10	Function
		Terminal resistance is applied.
	Shorted	Short only at the NT31/NT31C connected to the end of an
		RS-422A/485 cable.
		Terminal resistance is not applied.
	Open	Leave the terminals open when connecting an NT31/NT31C
		anywhere other than at the end of the RS-422A/485 cable.

Note Before connecting or disconnecting cables between devices, make sure that the power supply to all of the connected devices (NT31/NT31C, PC, etc.) is OFF.

Reference: S The internal circuit of the NT31/NT31C is shown below.

+ 10 (RDB)

−	16 (RDA)
	Terminal resistor (120 Ω)
	9 (TRM)

Making a connection here inserts a terminator between + (RDB) and − (RDA).

SFor details on setting the terminal resistance of the host unit, refer to setting methods for each type of the communication.

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