Embedded Modbus Library

Building upon the efforts undertaken to implement a primitive Modbus protocol interface for the IEC 61131-3 virtual machine environment, I have spent some time consolidating this development and have released an embedded Modbus slave protocol library.  This protocol library implements support for the most common Modbus operations including:

  • Read coils (function code 1);
  • Read discrete inputs (function code 2);
  • Read holding registers (function code 3);
  • Read input registers (function code 4);
  • Write single coil (function code 5);
  • Write single register (function code 6);
  • Write multiple coils (function code 15);
  • Write multiple registers (function code 16);
  • Write mask register (function code 22); and
  • Read write multiple holding registers (function code 23).

In this initial implementation, this library primary supports Modbus TCP operations – aligned with the initial implementation of Modbus operations on the IEC 61131-3 virtual machine – but there is scope for both Modbus RTU and Modbus ASCII implementations within the code base.  Additionally, this library has been implemented with a keen awareness of portability for different platforms and as such includes distinct APIs for database and target platform integration.

This embedded Modbus slave C library can be obtained from GIT at https://bitbucket.org/rob_au/modbus.  Similar to the IEC 61131-3 virtual machine project, this library is licensed under CC BY-NC 4.0.

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