Tx/Rx (+)
Tx/Rx (-)
Communication Common
Cable Shield
Termination Resistor Jumper JP1
Termination Resistor Jumper JP1 (detail)
FT3 Modbus
5
MODBUS WIRING
RS485 Wiring for Modbus
Wiring connections are made to terminal block TS5 for RS485 communication.
The Tx/Rx+ signal connects to pin 1, Tx/Rx- connects to pin 2 and communication common to
pin 3, and the cable shield to pin 4 as shown in Figure 3.1.
Termination Resistor
Connect a termination resistor across the receive/transmit signals of the last device on the
RS485 communication line. To connect the 121 ohm termination resistor on the FT3, set JP1 to
the TERM position.
Disconnect the termination resistor on all other external RS485 devices. The termination
resistor of the FT3 is disconnected by setting JP1 to the NC (Not Connected) position.
Fig. 3.1: RS485 Wiring
i
Note: JP1 jumper will either be in the NC or TERM position. It should be in the TERM
position on the last meter in the Modbus daisy chain.
RS485 Wiring: Modbus
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