Question

What will be the content of Accumulator, Register-B Overflow Flag (OV) after the execution of the following 8051 micro-controller assembly code?

MOV A, #65h

MOV 0F0h, #14h

DIV AB

DIV AB

1. A = 00h, B = 00h, OV = 1
2. A = 05h, B = 00h, OV = 0
3. A = 00h, B = 05h, OV = 0
4. A = 05h, B = 00h, OV = 1

Answer 1

Correct Answer - Option 2 : A = 05h, B = 00h, OV = 0

Concept:

DIV AB instruction

If the numerator ! = 0 → always makes CY = 0 & OV = 0

If the numerator = 0 → CY = 0, OV = 1 (indicates an error)

The operation of this instruction is shown below:

1. The DIV instruction divides the unsigned 8-bit integer in the accumulator by the unsigned 8-bit integer in register B.
2. After the division, the quotient is stored in the accumulator.
3. The remainder is stored in the B register.

Calculation:

Given contents of the accumulator and register are 65H and 14H respectively.

The values of the accumulator and the register B after DIV instruction executed two times are shown below after first and second-time execution respectively.

Instruction	Accumulator	Register B
DIV AB	04H	09H
DIV AB	00H	04H

 

OV = 0

Calculation:

Given contents of the accumulator and register are 65H and 13H respectively.

The values of the accumulator and the register B after DIV instruction executed two times are shown below after first and second-time execution respectively.

Instruction	Accumulator	Register B
DIV AB	05H	00H
DIV AB	05H	00H

 

OV = 0