5-4
Industio
CI-134 Series User’s Manual
Impedance Matching and Termination Resistors
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.
Industio
CI-134 already installs the resistors on board for your convenience,
indicated as follows. The value of the termination resistor should equal the
characteristic impedance of the transmission line. Resistors should be added near the
receiving side.
CI-134
RS-422/485 Device
2
TxD+(B)
RxD+(B)
1
TxD-(A)
RxD-(A)
3
RxD+(B)
TxD+(B)
4
RxD-(A)
TxD-(A)
7
RTS+(B)
CTS+(B)
6
RTS-(A)
CTS-(A)
8
CTS+(B)
RTS+(B)
9
CTS-(A)
RTS-(A)
Note:
Stands for termination resistor near the receiving side
Termination Resistor Jumper for Port 2
Termination Resistor Jumper for Port 4
Termination Resistor Jumper for Port 1
Industio
CI-134 Series Board
Data Mode Switch
ON
ON
1 2 3 4
CAP Jumper
JP1
ON
1 2 3 4
JP3
JP4
JP6
JP5
Interface Switch
Termination Resistor Jumper for Port 3
