Optimization of Mixed Reading of Binary and Register Variables in Modbus Protocol from PLC Implementing CPDev

Efficient communication is crucial for the proper operation of distributed automation systems. The article focuses on one of the aspects of such communication, related to the mixed reading of binary and register variables from the PLC controller in the Modbus RTU protocol. The research assumed a memory architecture with common addressing of variables of different types, allowing reading binary variables not only using dedicated bit functions (such as FC1), but also Modbus register functions (such as FC3). Such an architecture occurs, e.g., in controllers implementing the CPDev engineering environment. The article proposes a method of appropriate grouping of variables, leading to a reduction of the total communication cycle time. An optimization model has been implemented to automatically find the optimal grouping. Experiments were carried out and the obtained results were discussed. The results of the conducted research will be used in the development of the CPDev engineering environment.