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+2 votes
In base index addressing mode how many number of cycles for operand fetch is to be required?

is it 8 ?


4cycles =consumed for memory reference

2 cycle = consumed for arithmetic operations

1cycle =consumed when operand present in register

0 cycle = consumed when operand present in instruction itself



Add R3, (R1 + R2)

R3 <- R3 + M[R1+R2]

Useful in array addressing:
R1 - base of array
R2 - index amount
asked in CO and Architecture by Loyal (7.4k points) | 222 views
R3<- R3+ M[R1+R2]

for fetching data from R1 and R2 we need 1+1= 2 cycles .

Now we have to add the value of R1 and R2 (which will give us the memory location where the operand is present) which will take 2 cycles( arithmatic operation).

Now we have to fetch the operand from memory which will take 4 cycles.

Now we have one operand and we need the second operand for addition operation i.e. R3

fetching R3 will take 1 cycle.

so total cycles=2+2+4+1=9 cycles.
I think you forgot to count 2 cycles to sum with R3.
we need to count the cycles for operand fetch only. We have both operands available for addition now so the instruction can execute further.
oh yes! I didn't see the question carefully.

@Manu Thakur @Gaurav Joshi how 4 cycle for operand fetch after the effective add. calculation?? Can you please help to understand this?

Now we have to fetch the operand from memory which will take 4 cycles.Ca

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