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) |
JP5:Interface selection Jumper for Port 1
RS-422
RS-485
JP5
RS-422
RS-485
JP6
JP1 
JP2 
JP4 
JP3 
JP6:Interface selection Jumper for Port 2 |
RS-232 | SW2 | | SW1 | | | SW1: RS-422/RS-485 Selection Switch for Port 1/2/3/4 |
AUTO | | RS-485 |
| ON | | | | O | | | SW2: Data Mode Switch for Port 1/2/3/4 |
| | | | | N | | | |
1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | |
JP1/2/4/3:Termination Resistor Jumper for Port 1/2/4/3
Industio CP-114 Series Board
5-6Industio CP-114 User's Manual
