8051 direct addressing to read internal RAM Which instruction copies the byte stored at internal RAM address 04H into the accumulator A?

Introduction / Context:
Direct addressing allows the 8051 to access internal RAM or SFR locations by their absolute addresses. Reading a byte from a low RAM address into the accumulator requires the correct operand order and addressing form. This question tests recognition of the direct address form for a memory to register transfer.

Given Data / Assumptions:

• Internal RAM address of interest is 04H, within the lower 32 bytes used for register banks and general RAM.
• Destination register is A, the accumulator.
• MOV instruction supports register and memory operands.

Concept / Approach:

To read memory into A using direct addressing, use MOV A, direct_address. To write A back to a memory location, reverse the operands. Labels such as L4 represent assembler symbols, not numeric addresses, unless explicitly defined.

Step-by-Step Solution:

Verification / Alternative check:

In a simulator, preload 04H with a known value such as 5AH and execute MOV A, 04H. The accumulator updates to 5AH, confirming the correct semantics.

Why Other Options Are Wrong:

MOV A, L4: depends on a label and is not guaranteed to be 04H.

MOV L4, A: writes from A to memory, opposite of what is required.

MOV 04H, A: also writes A to address 04H rather than reading.

Common Pitfalls:

Reversing operand order, forgetting that direct addresses below 80H refer to internal RAM rather than SFRs, and confusing labels with numeric addresses.

Final Answer:

MOV A, 04H