The “Brain†of a PLC.
1.Controlled by a program called the executive or operating system (OS).
2.The executive is a collection of supervisory programs permanently stored in memory.
The CPU consists of following blocks :
1.Arithmetic Logic Unit (ALU),
2.Internal memory of CPU
3.Internal timers ,counters and Flags .
The various operations performed are :
1.Scanning I/O bus traffic control,
2.Program execution,
3.Peripheral and External device communication,
4.Data handling and self diagnostics.