Moxa Technologies CP-132U Series ユーザーズマニュアル

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Connection Cables and Cables Wiring 
CP-132U Series User’s Manual    5-7
Impedance Matching and Termination Resistors 
When using RS-422/485 serial communications, an electrical signal that travels through 
two different resistance junctions in a transmission line will sometimes give rise to signal 
reflection due to the impedance mismatch. Signal reflection causes signal distortion, which 
in turn contributes to communication errors. The solution to this problem is to establish the 
same impedance at the ends of the transmission line, as in the line itself, by terminating the 
ends of the line with resistors.