Hardware interfaces are designed to transmit status information at certain events (e.g. "valve gate open", "automatic switchover to holding pressure" or "separate reject part").
Communication interfaces are used to read an write actual and set values based on a communication protocol (such as Euromap, SPI or manufacturer specific protocols). This involves for instance injection speed profiles, holding pressure profiles or hotrunner nozzle temperatures.
In principle all parameters defined in the protocol maybe sent and received.