Network Termination

MAP450D

The com-link cable must be properly terminated to reduce the amount of interference and noise pickup from the surrounding environment. This is accomplished by using a termination circuit at both ends of the network cable. The following figure shows a typical termination circuit. The host termination is only needed if the host controller’s RS-422/485 adapter does not contain any built-in terminator circuitry. The end termination must be done at the extreme end of the com-link cable.

HOST

TERMINATOR

OIT3600

MAP460D

OIT3160

HOST TERMINATION

	Vcc
	Tx+
	Tx-
		470 Ohm
		to
	Rx+	10 KOhm
	Rx+	120 Ohm
		120 Ohm
		to
	Rx-	240 Ohm
	Rx-	470 Ohm
		470 Ohm
		to
	SIGNAL GND	10 KOhm
	SIGNAL GND
	CHASSIS GND
		EARTH
		GROUND

FROM HOST +

FROM HOST -

TO HOST +

TO HOST -

SIGNAL GND SHIELD

END TERMINATION

120Ohm

240Ohm

DO NOT

CONNECT

Network Grounding

To communicate properly, serious attention must be paid to the grounding scheme of the devices connected to the com-link. Improper grounding, improper termination, and faulty shielding of the com-link are the most common causes of system failure in a multidrop network.

		Shield
	Signal Ground	Signal Ground
	From Host +	From Host
	From Host -	From Host
	From Host -
	To Host +	To Host
	To Host -	To Host
	To Host -
	Shield
	To OIT	To OIT

1010-0046A, REV 00

B&B Electronics MAP450D installation manual Network Termination