Instruction or Operand Fetch

Question

Consider the following μ-program?

 

 

 

 

Which of the following operation is performed by above μ-program?

A. Instruction fetch

B. Direct operand fetch

C. Interrupt sub program initiation

D. Indirect operand fetch.

Ans. B

Please Specify proper reason.

My Doubt is in option B and D why D isnt the answer ?

 

Comments

Observe $I_1 \ and \ I_2.$
Instruction $I_1$ says to load the address specified by address field of Instruction register (IR) into $MAR.$
$I_2$ says that load MBR with the data which is stored at the memory location specified by $MAR$.

For indirect operand fetch, microprogram will be like -
$MAR \leftarrow IR[addr]\\MBR \leftarrow M[MAR]\\IR[addr] \leftarrow MBR\\MAR \leftarrow IR[addr]\\MBR \leftarrow M[MAR]$

Answer 1

In operand fetch we take a value from memory with help of instruction register(IR) and put into ALU operand ( TR,ACC).