The complete computer description includes both, the instruction cycle and the interrupt cycle. Interrupt cycle because there may arise a case of I/O operation anytime during normal operation. Instruction cycle because in absence of interrupts, the CPU is always busy with stored program instructions. A flip flop R is used as a condition to determine the type of operation. When R=0, the instruction cycle continues. Similarly when R=1, the computer goes through an interrupt cycle. Here it must be noted that an interrupt is signaled by IEN and R is just to make it sure that another interrupt does not get entertained while processing of an interrupt.
Consider the following diagram:
A basic computer consistes f the following hardware components:
Control functions and microoperations for a basic computer are as follows: