OpenPLC uses the Modbus/TCP protocol for SCADA communication. Modbus is one of the most used protocols in industry, is open source and royalty-free. This makes OpenPLC compatible with virtually any SCADA software in existence.
Modbus has mainly 4 functions, each one responsible for reading or writing to a specific I/O. The I/O address space on the OpenPLC is mapped to the Modbus address space according to the table below:
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MODBUS ADDRESS MAPPING
OpenPLC also provides a separated address space for memory variables with support for 16, 32 and 64 bit variables. The memory address space is detailed on the table below: