8051 assembly immediate vs direct addressing for moving an 8-bit constant into A Which instruction correctly loads the hexadecimal constant 27H into the accumulator A?

Introduction / Context:
In 8051 assembly programming, understanding addressing modes is fundamental. The accumulator A is the primary register for arithmetic and logic operations. Loading a constant value into A requires the correct use of the immediate addressing mode, which is denoted by the number sign. This question checks the ability to distinguish immediate, direct, and indirect addressing syntaxes for the MOV instruction.

Given Data / Assumptions:

• Target value is the 8-bit hexadecimal constant 27H.
• Destination register is the accumulator A.
• Instruction family is the 8051 MOV with various addressing modes.

Concept / Approach:

Immediate addressing loads a literal constant into a register using the format MOV dest, #immediate. Direct addressing without the number sign reads from an internal RAM or SFR address. Indirect addressing uses a register pointer such as @R0 or @R1, not a literal number.

Step-by-Step Solution:

Verification / Alternative check:

Assemble and simulate: MOV A, #27H results in A = 27H immediately after execution. Using MOV A, 27H would depend on memory contents at address 27H, which may differ from 27H.

Why Other Options Are Wrong:

MOV A, P27: operand is not a valid 8051 symbol here; incorrect syntax.

MOV A, 27H: direct addressing reads from data memory address 27H, not a literal constant.

MOV A, @27: @ requires R0 or R1 as a pointer, not a literal numeric address.

Common Pitfalls:

Forgetting the number sign in immediate mode, misreading direct address values as constants, and using incorrect indirect syntax are frequent mistakes.

Final Answer:

MOV A, #27H