Xylem 205546 Modbus Communication Modules for Displays - Manual (Page 13)

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Exampe ID settings
Unit #1 ID=1 and COM module offset ID=1 -> SRO ID=2 (1 + 1)
Unit #2 ID=1 and COM module offset ID=2 -> SRO ID=3 (1 + 2)
Unit #3 ID=4 and COM module offset ID=3 -> SRO ID=7 (4 + 3)
Termination
Modbus RS 485 communication requires bus termination. If the PLC is termi-
nated, unit #1 must be set in “OFF” position, unit #2 in “OFF” position and unit
#3 in “ON” position.
If, on the other hand, the PLC is NOT terminated, unit #1 must be set in “ON”
position.
2. Communication Modules
Modbus Communication Modules