Question

Consider the following program segment for a hypothetical CPU having three user registers R1, R2 and R3.

Instruction Operation Instruction
Size
(in words)

MOV R1, 5000 ; R1 $\leftarrow$ Memory [5000] 2

MOV R2, (R1) ; R2 $\leftarrow$ Memory [(R1)] 1

ADD R2, R3 ; R2 $\leftarrow$ R2 + R3 1

MOV 6000, R2 ; Memory [6000] $\leftarrow$ R2 2

HALT ; Machine halts 1

Consider that the memory is word addressable with size 32 bits and the program has been loaded starting from memory location 1000 (decimal). If an interrupt occurs during the ADD instruction, what will be the return address pushed on to the stack.

• A. 1005
• B. 1004
• C. 1007
• D. 1016

Answer 1

The correct option is B 1004

________________________________________
Instruction Instruction Location
Size (decimal)
________________________________________

$MOV{R}_1,5000$ 2 1000 to 1001

$MOV{R}_2,\left(R_1\right)$ 1 1002

$ADD{R}_2,R_3$ 1 1003

$MOV6000,R_2$ 2 1004 - 1005

$Halt$ 1 1006
___________________________________

The return address pushed onto the stack is 1004.