Question

After execution of ANI 0FH with accumulator = A9H, which flags are affected ?

• A. Sign, zero and carry
• B. Carry and zero
• C. Zero and parity
• D. Sign, zero, parity and carry

Hint:

Logical instructions (AND, OR, XOR) always clear the Carry and Auxiliary Carry flags (though 8085 is an exception for AC). Sign, Zero, and Parity always reflect the result.

Answer 1

The Correct Option is D

The instruction ANI (AND Immediate) in 8085/8086 microprocessors performs a bitwise logical AND operation between the accumulator and an 8-bit immediate value. 1. Executing the Operation: Accumulator = $A9H = 1010 \ 1001_2$ Immediate Value = $0FH = 0000 \ 1111_2$ Perform bitwise AND: $1010 \ 1001$ (A9H)
$\text{AND } 0000 \ 1111$ (0FH)
$0000 \ 1001$ (09H) The new value in the accumulator is $09H$. 2. Flag Behavior for Logical Instructions: In 8085/8086, logical instructions like ANI affect specific flags:
• Carry Flag (CY): Always cleared (set to 0) by logical instructions.
• Auxiliary Carry (AC): For ANI, it is usually set (logical instructions set or clear it depending on the specific processor architecture).
• Sign (S), Zero (Z), and Parity (P): These are updated based on the result of the operation. 3. Analyzing Affected Flags: Since logical operations modify the status of the processor, the Carry, Zero, Sign, and Parity flags are all recalculated or specifically reset. While Carry is always 0, it is still "affected" (reset) by the execution of the instruction.