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Chapter 3 Product specification
3-5
3.4 Terminating resistance
For communication via RS-422 channel, terminating resistance from external must be connected. Terminating resistance
has the function to prevent distortion of signal by reflected wave of cable for long-distance communication, and the same
resistance (1/2W) as characteristic impedance of cable must be connected to terminal of network.
When using the recommended cable in 3.3, connect terminating resistance of 120
Ω
to both ends of cable. Also when
using other cable than recommended, the same resistance (1/2W) as characteristic impedance of cable must be
connected to both ends of cable.
1)
How to connect terminating resistance during RS-422 connection
GM3/4/6 unit
GM7 unit
RXA
RXB
TXA
TXB
·
SG
·
PLC #1 PLC #2 PLC #(N-1) PLC #N
RXA
RXB
TXA
TXB
·
SG
·
RXA
RXB
TXA
TXB
·
SG
·
RXA
RXB
TXA
TXB
·
SG
·
PLC #1 PLC #2 PLC #(N-1) PLC #N