Moxa Technologies CP-114 Series - Manual (Page 46)

5-6 Industio CP-114 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-114 Series 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. Note: Stands for termination
resistor near the receiving side.
CP-114 Series 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)
JP1
JP2
JP4
JP3
Industio CP-114 Series Board
ON
1 2 3 4
O
N
1 2 3 4
RS-232 RS-422
RS-485
JP5
RS-232 RS-422
RS-485
JP6
By RTS RS-422
SW2 SW1
AUTO RS-485
JP1/2/4/3:Termination Resistor Jumper for Port 1/2/4/3
JP5:Interface selection Jumper for Port 1
JP6:Interface selection Jumper for Port 2
SW1: RS-422/RS-485 Selection Switch for Port 1/2/3/4
SW2: Data Mode Switch for Port 1/2/3/4