CPU Consist of Follwing Blocks

1) Arithmetic logic unit (alu)
2) Program memory( EEprom,Eprom,Rom,Ram)
3) Process image momery(internal memory)
4) Internal timer and counter
5) Flags or status bits/files


INPUT MODULE:-
Input module act as an interface between the field control input and the cpu. Voltage/current genenret by the senser,transducers,limit switeches,push botton etc. applied to terminal of i/p module.


OUTPUT MODULE:-
Output module act as a llink between the cpu and the output device located in the fields devices.
Field device coueld be relays contactor, lamps, motorized,acuators,solenoied valve,etc. these device actually control the process.
It converts the output signal delived by cpu into an appropariate voltages level; suitabal for the output.Output signal is decrite or analog.