User`s manual

Connection Option (Opt8x) and Cable Wiring
Smartio C168H/PCI User’s Manual 5-13
RS-485 Device N
Slave
Data+(B)
Data–(A)
GND
See the section RS-485 Programming in the chapter Serial Programming Tools for
more details on Opt8J RS-485 programming.
RS-422/485 Impedance Matching
When using RS-422/485 serial communications, an electrical signal travels through
two different resistance junctions in a transmission line. The impedance mismatch
that exists will sometimes cause signal reflection, distorting the signal. This in turn
contributes to 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 resistance of the termination resistor should equal the characteristic impedance
of the transmission line. Resistors should be added near the receiving side.
Opt8J/F/Z RS-422/485 Device
3 TxD+(B) RxD+(B)
16 TxD–(A) RxD–(A)
2 RxD+(B) TxD+(B)
14 RxD–(A) TxD–(A)
5 RTS+(B) CTS+(B)
13 RTS–(A) CTS–(A) Opt8J only
4 CTS+(B) RTS+(B)
19 CTS–(A) RTS–(A)
Note:
1. represents a termination resistor near the receiving side