Network Termination

The com-link cable must be properly terminated to reduce the amount of

interference and noise pickup from the surrounding environment. This is

accomplishedby 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-linkcable.

Network Grounding

Tocommunicate 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

systemfailure in a multidrop network.

12 MAP450D

1010-0046A,REV 00ShieldSignalGroundFromHost +ToHo st +ShieldTo OIT To OITSignalGroundFromHostToH ostFromHost -ToHo st -
HOSTTERMINATION
470Ohm
to
10KOhm
Tx+
Tx-
Vcc
Rx+
Rx-
SIGNALGND
CHASSISGND
EARTHGROUND
TERMINATOR
HOST
OIT3600
120Ohm
to
240Ohm
FROMHOST +
FROMHOST -
TOHOST +
TOHOST -SIGNALGNDSHIELD
DONOT
CONNECT
ENDTERMINATION
470Ohm
to
10KOhm
120Ohm
to
240Ohm
MAP460D OIT3160
TERMINATOR