Six communication modules for use with FX3U PLCs. The ADP modules fit on to the left hand side of the base unit while the BD modules clip into the front left corner of the base unit. The RS232 interfaces can be used for applications such as communication with a PC, printer or bar code reader while the RS422 interfaces provide a second programming port which enables an operator panel (HMI) and a programming PC to be connected at the same time. The RS 485 interfaces allow networking of FX PLCs and a simple way of connecting to Mitsubishi inverter drives using the built-in protocol instructions. The USB BD module offers connectivity to PCs via USB for programming purposes.