Consider addition of two numbers when CPU uses $2's$ complement form: $$ 1\ 1\ 0\ 0\ 0\ 0\ 1\ 1\\0\ 1\ 0\ 0\ 1\ 1\ 0\ 0\\-------\\0\ 0\ 0\ 0\ 1\ 1\ 1\ 1\\------- $$

$$Carry\ = 1,\ Overflow = 0, \ Zero Flag = 0$$

My Reasoning:

  • Zero Flag isn't set because the result isn't zero
  • Overflow isn't set because Carry in = Carry out

However, the answer says that Zero Flag is set $(ZF = 1)$, Am I going wrong ?


  • Got ZF/Carry/Overflow info from Here
  • $\begingroup$ Your question already includes a complete answer to the original problem but no question about this answer. Thus, only "yes/no" answers may remain, helping neither you nor future visitors. Please read related meta discussions here and here and adjust your question accordingly, e.g. by formulating a specific question about a single element of your answer you are uncertain about. If you just want general feedback, you are welcome to visit us in Computer Science Chat. $\endgroup$ – Raphael Feb 28 '15 at 16:27

However, the answer says that Zero Flag is set (ZF=1), Am I going wrong ?

No, you are correct. If the result is not zero, and in this case it is not, the zero flag is not set.

  • $\begingroup$ Yeah, I too felt the same $\endgroup$ – SimpleGuy Dec 30 '14 at 11:42

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