Advantech UNO-1170E user manual Terminal Resistor Setup for RS-422/485

2.3.5 Terminal Resistor Setup for RS-422/485

The onboard termination resistor (120 Ohm) for COM2/COM3 can be used for long distance transmission or device matching. (Default Open.) Each terminal resistor responds to different channels for RS-422/485.

Usually, these resistors are needed for both ends of the communication wires and the value of the resistors should match the characteristic imped- ance of the wires used.

Table 2.3: Terminal Resistor Settings

COM port	Switch No.	Pin	Setting	Description
COM3	SW3	1	ON	120 Ohm between Data+/
				Data- (RS-485)
				Or 120 Ohm between Tx+/Tx-
				(RS-422)
			OFF	Open (Default)
		2	ON	120 Ohm between Rx+/Rx-
				(RS-422)
			OFF	Open (Default)

2.3.6RS-485 Auto Flow & RS-422 Master/Slave Mode

You can set the “Auto Flow Control” mode of RS-485 or “Master/Slave” mode of RS-422 by using the SW2 DIP switch for each RS-422/485 port.

In RS-485, if the switch is set to “Auto”, the driver automatically senses the direction of the data flow and switches the direction of transmission. No handshaking is necessary.

In RS-422, if DIP switch is set to “On,” the driver is always enabled, and always in high or low status.

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