PLC I/O modules are one of the three core components that operate a programmable logic controller. I/O refers to input/output. PLC I/O modules act as messengers between a processor and an I/O device.
PLC I/O modules assist the data exchange between an external device and computer memory. Their main job is to process communication to the PLC and accept commands sent from a processor. They can also detect errors, run status reports and co-ordinate a timely flow of data.
The type of PLC I/O modules used by a programmable logic controller depends on the type of input device. These are categorised as input or output types. Some PLCs respond to digital inputs and outputs, whereas others respond to analog signals. Digital inputs are either on or off, and analog signals process conditions as voltage. Other types include discrete, speciality and communication modules. Smaller PLCs are usually designed with fixed I/O points.