What is remote i/o

Simply speaking, remote i/o is a data acquisition/transmission module with communication function, which has no control and adjustment function. Only send the field data to the control center (such as PLC), or receive the data from the control center to control the field equipment.
There are many communication modes, and each manufacturer has its own standards, such as free port communication, PROFIBUS, MODBUS, etc.
Example: operation console; Operation console buttons and indicator lights.
In the past, control cables were used to connect with PLC. If remote i/o is adopted, it can be connected with PLC through a communication line, saving wiring and i/o points of PLC