IHMI-PLC virtual-PLC technology can be incorporated to extend HMI software functionality. It includes a stand-alone development system for Windows PC and virtual-PLC Runtime for Windows PC and CE platforms as well as a designer, which allows users to create PLC control programs using any mix of three of the IEC61131-3 programming languages. The same compiled PLC control program can run on the Windows PC or CE platform. The PLC supports Modbus protocol as a communication interface, so any HMI can access and control all PLC variables of interest and monitor and control the values in registers, coils, digital I/O and analog I/O.