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+3 votes

The contents of the flag register after execution of the following program by 8085 microprocessor will be

MVI B,(01)$_H$

  1.  (54)$_H$
  2. (00)$_H$
  3. (01)$_H$
  4. (45)$_H$
in CO and Architecture by Active (4.9k points) | 4.4k views
please anybody explain this question.I tried allot but unable to understand it.
m also getting 45h,,,,if v try to use again dcr will result into 95h

5 Answers

+9 votes
Best answer

My Answer: None of These, ISRO Answer: (a)

Explanation: 8085 microprocessor has a 8 bit flag register to indicate certain conditions arising after arithmetic and logical operations or to control certain operations.

8085 flag register

  • Carry flag indicates whether there is carry or not after an arithmetic and logical operation.
  • Parity flag indicates whether the result contains odd number of 1s or even number of 1s.
  • Auxiliary carry (or half carry) flag indicates that is there carry from the 3rd bit to 4th.
  • Zero flag indicates whether the result of an arithmetic or logical operation is zero or nonzero.
  • Sign flag indicates whether the result is positive or negative.
  • Other bits in this register are undefined.
Lets traverse the program:
  • SUB A: subtracts the content of accumulator (A) from the content of the accumulator (A); Content of A will become (00)H; Flag Register: 0100 0100 because result is zero and result contains 0 (even) number of 1s.
  • MVI B, (01)H : stores 01 in register B; No computation, no change in Flag Register.
  • DCR B: decreases content of register B; Content of B will become (00)H; Flag Register: 0100 0100 because result is zero and result contains 0 (even) number of 1s and DCR/INC don't affect the carry flag in 8085. 
So, flag register after execution will be 0100 0100 = (44)H.
by Active (2.4k points)
edited by
Another wrong thing in question - other bits are undefined- so we can't say it is 0.

Auxilary carry will be 1 after the decrement of (01)H

oooo ooo1 (original B)

1111 1111   (substracting 1) 


here auxilary carry will be 1 on decrement. so yeah. Isro is correct.

+2 votes

According to virtual 8085 processor , answer is 45H
please check

by Active (4.1k points)
+1 vote
ans is a.(54)h

can any one explain iam getting doubt..?
by Active (4.9k points)
+1 vote

I ran this code in 8085 simulator and step in each step and Got o/p = (45)h as flag value.. Arjun Sir could you explain ...

ISRO 2015 Qtn

by Active (1.5k points)
I have also doubt in this q? Arjun sir please explain this?
Are you sure you did the execution correctly? Because then the control should be at HLT instruction. Also, CY at end must be 0 here.
0 votes
Ans is (54)H OPTION A
by (11 points)
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