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Figure 12: Modbus RS-485 biasing switch on the ProtoNode N34
RS-485 bias switch
3.2.1 - Biasing the Modbus RS-485 network
•
An RS-485 network with more than one device must have biasing to ensure proper communication. The biasing must be done on
one device.
•
The ProtoNode has a 510 Ohm resistor switch that is used to set the biasing. The ProtoNode’s default position for the Biasing switch
is OFF from the factory.
•
The biasing MUST always be left in the OFF position. The OFF position is when the two (2) RED biasing jumpers straddle the four
(4) pins closest to the outside of the board of the ProtoNode. See Figure 12.
• It is recommended that the biasing be left in the OFF position unless there is a problem with communicating with more
than one device. If this occurs, try setting the biasing to ON.
Figure 11: Power and RS-485 connections
Device pins
ProtoNode 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
3.2 - Wiring connections
The following shows the wiring connections to ProtoNode RER (FPC-N34 BACnet).
ProtoNode 6-pin Phoenix connector: Pin outs to Modbus RTU products
•
ProtoNode RER (FPC-N34 BACnet) has a 6-pin Phoenix connector. Pins 1 through 3 are for Modbus RS-485 to the devices and
pins 4 through 6 are for power.
3 - Interfacing ProtoNode to Devices (cont.)
