Question

A.Write a program fragment that will set the sign flag

B.Write a program fragment that will set the overflow flag.

C. Write a program fragment that sets the zero flag.

D.What will be the value of the parity flag after the following lines execute?

Mov al, 3

Add al, 5

Answer 1

Given, Write a program to show sign, overflow and zero flag set using fragment code.

Assume we have AX and BX register fill with 7FFFh and we want to add.

ADD AX, BX

Binary value of 7FFFh => 0111 1111 1111 1111

0111 1111 1111 1111 + 0111 1111 1111 1111 => 1111 1111 1111 1110 (FFFE)

[A]. In the above example the sign flag will be set since MSB bit is 1.

[B]. To set overflow flag add two same bit position number.

example.

Mov BX, 05h

Mov Ax, 05h

ADD Ax, Bx

0100 + 0100 => 1000 (overflow bit flag will be turned on)

Sum of these number yield a sign bit .

[C]. Zero flag get turned on when the value of the result becomes all 0.

MOV BX, 05h

MOV AX, 05h

SUB AX, BX

0100 - 0100 => 0000 (0)

The above instruction result in all 0 bits and hence zeos bit flag will turned on.

[D]. Mov al,3

Add al,5

binary of 3 is 011 and binary of 5 is 101

adding 011 + 101 => 1000 (8)

As in result we can see we have a odd set bit so the parity flag will be 0.

Let me know if you need more help in this.