Figure 52: Rs-485 Communication Wiring - ABB 266 MODBUS User Manual

RS-485 wiring connections
Reversed polarity for the Bus + and Bus - connections will cause the transmitter to not communicate to the Host device even
though all communication parameters are correct.
1. Verify that the communication wiring Bus (+) is wired to COMM A (+), Bus (-) is wired to COMM B (-), and that the terminal
connections are tight (Figure 52).
2. If multiple transmitters are part of the same RS-485 Bus, then each must be checked for proper wiring connections and
that the last unit is properly terminated. If communication has been restored, it is not necessary to continue this procedure.
3. If the transmitter is still experiencing a communication failure, the terminal block should be replaced. Go to section 5.7,
Replacing the terminal block, for replacement instructions.
4. If after replacing the terminal block, the transmitter is still experiencing a communication failure, contact customer service.
Customer service contact information may be found in section 6.4.2, Customer services.
RS-485 COMM
Bus + A (+)
Bus - B (-)

Figure 52: RS-485 communication wiring

266 MODBUS® multivariable transmitter User manual 2105216 Rev. AB | 77
6 Troubleshooting