q explain the fetch cyclethe beginning of every

Question

Q. Explain the Fetch Cycle?

The beginning of every instruction cycle is the fetch cycle and causes an instruction tobe fetched from memory.  

The fetch cycle comprises four micro-operations which are executed in three timing steps. The fetch cycle can be written as:

T1:  MAR ← PC

T2:  MBR ← [MAR]

         PC    ← PC + I

T3:  IR      ← MBR

Where I is the instruction length. We presume that a clock is available for timing purposes and that it produces regularly spaced clock pulses. Every clock pulse defines a time unit. So all the units are of equal duration. Every micro-operation can be performed within the time of a single time unit. Notation (T₁, T₂, T₃) represents successive time units. What is done in these time units?

• In the first time unit the content of PC is moved to MAR.
• In the second time unit contents of memory location specified by MAR is moved to MBR and contents of PC is incremented by I.
• In the third time unit content of MBR is moved to IR.