UGC NET CSE | January 2017 | Part 2 | Question: 34

Question

The contents of Register $(BL)$ and Register $(AL)$ of $8085$ microprocessor are $49H$ and $3AH$ respectively. The contents of $AL$, the status of carry flag $(CF)$ and sign flag $(SF)$ after executing $'SUB AL, BL'$ assembly language instruction, are

• A. $AL=0FH; \: CF=1; \: SF= 1$
• B. $AL = F0H; \: CF = 0; \: SF = 0$
• C. $AL =F1H; \: CF = 1; \: SF= 1$
• D. $AL =1FH; \: CF=1; \:SF=1$

Comments

is it option 3?

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y some1 named @Psunny is downvoting my questions one after another? :\

Answer 1

 Answer is option C.

AL = F1H, CF = 1,  SF = 1.

Answer 2

AL - 3AH.      

BL - 49H

The given instruction is to subtract the contents of BL from AL.

0011 1010 -

0100 1001

---------------------

 1111 0001

Sign flag S=1

Carry flag CY=1

result= F1H

Sign flag is set since the produced result is negative.

Since the first operand is less than the second operand, the carry flag is set.

Answer 3

(A) => 3AH => 00111010
(B) => 49H => 01001001
                         ------------------
                          11110001
(A) => F1H
(CY) => 1
(S) => 1

The carry flag is set since the first operand is less than the second operand.
Since the result produces the negative result sign flag is set