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E204701
2-12
2: Using the ProtoCom/ProtoCom-Lon
2.6.1: Biasing the Modbus RS485 Network (only if necessary)
An RS485 network with more than one device needs to have biasing to ensure proper
communication. The biasing only needs to be done on one device. If necessary, you
can set up biasing on the ProtoCom. Refer to Section 1.8 for instructions on removing
and replacing the unit’s top cover.
The ProtoCom has 510 Ohm resistors that can be used to set the biasing. The default
position of the Biasing jumpers is OFF. The OFF position is when the 2 RED biasing
jumpers straddle the 4 pins closest to the outside of the board of the ProtoCom. To
turn biasing on, move the jumpers to the right so that they straddle the four inside
pins. See the figure below.
Figure 2.6: Biasing Jumpers
IMPORTANT!
• Only turn biasing ON if the Building Management System (BMS) cannot see more
than one device connected to the ProtoCom and you have checked that all of the
settings (Modbus COM settings, wiring, and DIP switches) are correct.
• Do not touch any other parts of the main board.
To turn biasing
ON, move the
red jumpers to
the right so
that they cover
these 2 pins