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RS485 Wiring Diagram from an M1E Port 2 (DB9) to an LULC031 Modbus Interface

Goals and Symptoms

The purpose of this resolution is to inform Momentum Processor and TesysU users how to wire an LULC031 to a Momentum Processor via its Port 2 RS485 (DB9 connector) for proper communications.

Facts and Changes

In order to communicate from the M1E to the LULC031 (using the XMIT or XXMIT Function Block), two 470 ohm biasing resistors from the + and - RS485 lines must be added and connected to a 5vdc power supply (required by the LULC031). When communications between the M1E and LULC031 are first initiated, it will take approximately 20 seconds for the communication parameters of the LULC031 to initialize. If the communication parameters do not change and the LULC031 was power cycled, communications will immediately be established and no initialization is necessary. If the communication parameters are changed and the LULC031 is power cycled, initialization will re-occur for another 20 seconds to adjust to the new parameters.


  • 120 ohm termination resistors must also be added at each end of the RS485 network.

Causes and Fixes

Wiring diagram.


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