Question

Consider the flags in flag Register from left to right :
A. S

B. Z

C. AC

D. P

E. CY

Choose the correct answer from the options given below :

• A. A, B, C, D, E
• B. A, B, D, C, E
• C. C, D, E, A, B
• D. C, D, A, B, E

Hint:

Use the mnemonic "S-Z-X-AC-X-P-X-CY". Just remember that Sign is always the MSB and Carry is always the LSB in almost every standard microprocessor architecture.

Answer 1

The Correct Option is A

Concept:
• In the 8085 microprocessor, the Flag Register is an 8-bit register where specific bits represent the status of the ALU after an operation.
• "Left to right" in register notation means from the Most Significant Bit (MSB) to the Least Significant Bit (LSB).

Step 1: Identify the 8085 Flag Register Architecture
The bits are arranged as follows:
• Bit 7: S (Sign Flag)
• Bit 6: Z (Zero Flag)
• Bit 5: X (Undefined)
• Bit 4: AC (Auxiliary Carry Flag)
• Bit 3: X (Undefined)
• Bit 2: P (Parity Flag)
• Bit 1: X (Undefined)
• Bit 0: CY (Carry Flag)

Step 2: Arrange the given flags from Bit 7 to Bit 0
Scanning from left (Bit 7) to right (Bit 0), we find:
S (A) \(\rightarrow\) Z (B) \(\rightarrow\) AC (C) \(\rightarrow\) P (D) \(\rightarrow\) CY (E).

Step 3: Verify labels
The sequence A, B, C, D, E correctly maps to the physical layout of the status bits in the register.