Mitsubishi Electronics FX-485ADP, FX0N-485ADP manual Terminating resistances

2.3 Terminating resistances

The terminating resistances are resistances connected between terminals SDA and SDB, and between terminals RDA and RDB at both end stations of the circuit (or the interface when an interface such as 485PC-IF is used at both end stations), when connecting with the RS-485 or RS-422 circuit. For connection examples, see section 2.1 and 2.2.

Classification of terminating resistances

In this product, two sets of terminal end resistances (330 Ω ✕ 2, 110 Ω ✕ 1) are packaged, and the terminating resistances to be connected differ as shown below depending on the circuit being used.

●When communicating with the RS-422 circuit, connect the resistances of “330 Ω 1/4W ” as the terminating resistances.

●When communicating with the RS-485 circuit, connect the resistances of “110 Ω 1/2W ” as the terminating resistances.

〈330 Ω〉			〈110 Ω〉
	Orange	Brown			Brown	Orange
Two-pair wiring			One-pair wiring
	SDA	Terminating resistance		SDA
	SDB	(330 Ω)		SDB
	RDA	Terminating resistance		RDA		Terminating resistance
	RDB	(330 Ω)		RDB		(110 Ω)

2.4 Cautions for wiring

As one of the conditions for exhibiting the function of the 485ADP sufficiently and building up a reliable system, external wiring resistant to noise is essential. Cautions for external wiring are given below.

(1)In this system, the data is read or written (turned on or off by force) while the PC is operating. Accordingly, if abnormal data is written into the PC due to effect of noise, the PC may malfunction, leading to machine trouble or accident, and therefore the following cautions should be strictly observed.

●Never lay near or bundle together with the main circuit, high voltage line or load line. Or effects of noise or surge induction may be serious. Keep at least a safe distance of over 100 mm from these lines.

●Ground the shield wire or shield of shield cable at one point at the PC side. Never ground commonly with high voltage line.

(2)Terminals screws of terminal block for RS-485 are M3 threaded. Therefore, connect wiring by fitting a crimped terminal suited to the terminal screws (see below) to the cable.

6.2mm (0.24 inches) or less

M3		M3
threads	6.2 mm	threads
	(0.24 inches)
	or less

(3)Tightening torque of terminals is 0.5 to 0.8 N·m (5 to 8 kgf·cm). Screw terminals must be secure enough to prevent a loose connection from causing a malfunction.