Modbus Interface

In order to improve accessibility of the IEC 61131-3 virtual machine for external developers, I have committed code which provides a basic Modbus TCP protocol interface for the IEC 61131-3 virtual machine. The protocol was originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Since this time, this protocol has become the de facto standard for communication with a range of industrial devices including programmable logic controllers, data loggers and smart instrumentation.  See and

Medford Modbus Viewer

While this interface is still under development, the basic interface that is in place now allows for 16-bit integer values to be read from the virtual machine environment by external data visualisation packages – The package that I have used for evaluation purposes above is from This interface in turn provides a greater level flexibility for the monitoring of byte code under evaluation within the IEC 61131-3 virtual machine environment.


One thought on “Modbus Interface

  1. This is just a quick note to mention that this basic interface has been further updated to incorporate support for the writing of Modbus values (Write Single Register, FC6 and Write Multiple Registers, FC16) in the IEC 61131-3 virtual machine environment.

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