Hi Raghu,

What Hans is reffering to are the steps that the controller needs to take in order to execute a program instruction. This includes fetching the instruction, fetching the associated data (if any) and executing the instruction.
For example, even something as simple as PUSH ACC requires the controller to get the contents of the Accumulator, copy it to the memory location pointed to by the Stack Pointer and finally incrementing the SP.


Regards,
Rob.