Q. Explain Indirect Cycle in control unit?
Once an instruction is fetched the subsequent step is to fetch the operands. The instruction may have indirect and direct addressing modes. An indirect address is controlledemploying indirect cycle. The below micro-operations are needed in indirect cycle:
T1: MAR ← IR (address)
T2: MBR ← [MAR]
T3: IR (address) ← MBR (address)
The MAR is loaded with address field of IR register. Then memory is read to fetch the address of operand that is transferred to address field of IR through MBR as data is received in MBR during read operation.
So the IR now is in same state as of direct address viz as if indirect addressing hadn't been used. IR is now ready for execute cycle.