5-4
Industio CP-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
CP-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.
CP-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
1 2
ON
JP2
JP1
SW2
SW1
Industio CP-132 Series Board
1 2
ON