5-4
Industio
CI-132 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-132 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-132
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
Industio CI-132 Series Board
Interface Switch
ON
1 2
ON
1 2
CAP Jumper
JP1
JP3
JP4
Termination Resistor Port 2 Jumper
Termination Resistor Port 1 Jumper
Data Mode Switch
SW2
SW1
