Unitronics GW-BAC1 - Connecting PLC via Modbus RS-485

Unitronics’s BACnet Gateway User Guide Page 7 of 28
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2.2 Connecting a Unitronics PLC to the GW-BAC1 via Modbus RS-485
GW-BAC1 6 Pin Phoenix connector for RS-485 Device
 The 6 pin Phoenix connector is the same for GW-BAC1.
 Pins 1 through 3 are for Modbus RS-485 devices.
o The RS-485 GND (Pin 3) is not typically connected.
 Pins 4 through 6 are for power. Do not connect power (wait until Section 3.4).
Figure 2: Power and RS-485 Connections
Device Pins
GW-BAC1 Pin #
Pin assignment
Pin RS-485 +
Pin 1
RS-485 +
Pin RS-485 -
Pin 2
RS-485 -
Pin GND
Pin 3
RS-485 GND
Power In (+)
Pin 4
V +
Power In (-)
Pin 5
V -
Frame Ground
Pin 6
FRAME GND