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 GroundingTocommunicate 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
EARTHGROUNDTERMINATOR
HOST
OIT3600
120Ohm
to
240Ohm
FROMHOST +
FROMHOST -TOHOST +
TOHOST -SIGNALGNDSHIELDDONOT
CONNECT
ENDTERMINATION
470Ohm
to
10KOhm
120Ohm
to
240Ohm
MAP460D OIT3160
TERMINATOR