Flag register of 8085 microprocessor has five flags namely.

Question

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S, Z, AC, P, CY

Explanation: The 8085 microprocessor contains an 8-bit flag register known as the Program Status Word (PSW). It consists of five active status flags (S, Z, AC, P, and CY) that indicate the outcome of arithmetic and logical operations performed by the Arithmetic Logic Unit (ALU).

Working Principle: The Flag register tracks the status of the CPU after operations: S (Sign) reflects the MSB, Z (Zero) indicates if the result is zero, AC (Auxiliary Carry) tracks carries from bit 3 to bit 4, P (Parity) checks for even number of set bits, and CY (Carry) indicates an overflow beyond the 8-bit capacity.

Key Formulas: $PSW = [A, F]$ — The 16-bit register pair representing Accumulator and Flag status

Key Points: The 8085 Flag register is 8 bits wide but uses only 5 bits for status reporting.; The 3 remaining bits in the PSW are undefined/unused.; Sign flag (S) is 1 if the MSB of the result is 1 (negative).; Parity flag (P) is 1 if the result contains an even number of 1s.

Advantages: Efficient status monitoring of ALU operations.; Enables conditional jump instructions.

Disadvantages: Does not include an Overflow (OV) flag, unlike the 8086 microprocessor.

Applications: Conditional branching (e.g., JZ, JNC, JP).; Multi-precision arithmetic operations.

Additional Info: The 8085 does not have an overflow flag; overflow detection in 8085 must be manually calculated using logic.. Options B, C, and D are incorrect because they include an OV (Overflow) flag, which is not part of the 8085 architecture.

Answer: A is correct — The 8085 flag register comprises the Sign, Zero, Auxiliary Carry, Parity, and Carry flags.

Exam Tip: Always remember that the 8085 lacks an Overflow (OV) flag, which distinguishes it from the 8086 microprocessor; this is a very common trap in competitive exams.

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