User`s manual

5-12 Intellio C218Turbo User's Manual
RS-422/485 Impedance Matching
For RS-422/485 serial communications, when an electrical signal travels through two
different resistance junctions in a transmission line, the impedance mismatch will
sometimes cause signal reflection. Signal reflection causes signal distortion, which in
turn will contribute communication errors. The solution to this problem is to
establish the same impedance at the line ends as in the line itself by terminating them
with resistors.
The value of the termination resistor should equal the characteristic impedance of the
transmission line. The resistors should be added near the receiving side.
Opt8J/F/Z RS-422/485 Device
3TxD+(B) RxD+(B)
16 TxD-(A) RxD-(A)
2RxD+(B) TxD+(B)
14 RxD-(A) TxD-(A)
5 RTS+(B) CTS+(B)
Opt8J only 13 RTS-(A) CTS-(A)
4 CTS+(B) RTS+(B)
19 CTS-(A) RTS-(A)
Note:
1. Stands for termination resistor near the receiving side
2. The suggested termination resistor for AWG #26 cable is 100 ohm.
3. The suggested termination resistor for phone cable is 600 ohm.