Communication Protocol for Connecting an HMI to a PLC Check out the full blog post over at https://realpars.com/what-is-hmi/ HMIs and PLCs work together to monitor and control the machine. This means they have to be compatible and they also have to speak the same language so to say. This comes in the form of a Protocol which is just an industrial network. Engineers can program an HMI to perform almost any function that can be controlled or information that can be monitored by a PLC. #Automation