How many times does the NOP instruction execute in the following sequence? MOV C

Question

How many times does the NOP instruction execute in the following sequence?

                        MOV CX, 20H

XYZ:               PUSH CX

                        MOV CX, 9

ABC:               NOP

                        LOOP ABC

                        POP CX

                        LOOP XYZ

I understand the first loop executes 9 times but im torn between whether you multiply 9 by 20 or 32. 20 is in the problem but I have seen other solutions say 32. Is it 20 and 32 and if its 32 please explain why. Thanks

Explanation / Answer

So the problem here is to understand

what is the value of "20H"

"H" here means "Hexadecimal" or "Base 16"

Just like Decimal number system(10) we have other Hexadecimal Number system(16)

Basic mapping from decimal to Hexadecimal

0 - 0

1- 1

2-2

3-3

4-4

5-5

6-6

7-7

8-8

9-9

10-A (Note 10 in decimal is A in Hexa)

11 - B

12 - C

13 - D

14 - E

15 - F

Now for only letters till F is used So to represent the number from decimal now we use two hexadecimal digits.

Just like 675 in decimalis 10*10*6 + 10*70 + 1*5

this example is to convert hexadecimal to decimal

A34 = 16*16*A + 16*3 + 4

SO it GIVEN (20H) that is 2 hexa digits are used

So (20) = 16*2 + 0

which is 32 in decimal

So for practice here are some examples with solutions at the end

Convert following to decimal

1) 45H

2) ABH

3) 3CDH

SOLUTIONS

1) 16*4 + 5

2)16*A + B = 16*10 + 11

3)16*16*3 + 16*C + D = 16*16*3 + 16*12 + 13

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