8051 instruction — moving the value from Port 3 to register R2 Which instruction correctly transfers the current value present at Port 3 into general-purpose register R2?

Introduction / Context:
8051 supports register-to-direct, direct-to-register, and accumulator-based data moves. Knowing valid addressing forms helps avoid assembler errors and unintended side effects.

Given Data / Assumptions:

• We need to read a port's latch/pin value (Port 3) into a CPU register.
• Direct addressing of SFR P3 is permitted.
• Target register is R2 (in the current active register bank).

Concept / Approach:
The instruction format MOV Rn, direct is valid: it copies the byte at a direct address (such as SFR P3) into a working register Rn. Thus MOV R2, P3 transfers the Port 3 value into R2 in a single instruction.

Step-by-Step Solution:

Verification / Alternative check:
Referencing the 8051 instruction set shows opcodes MOV Rn, direct (A8–AF opcodes) are legal and execute in 2 bytes, 2 machine cycles on many variants.

Why Other Options Are Wrong:

• MOV P2, R3: writes R3 to Port 2, wrong direction and wrong port.
• MOV R3, P2: reads Port 2, not Port 3, and puts it in R3, not R2.
• MOV 3P, R2: invalid mnemonic/syntax.

Common Pitfalls:
Forgetting that ports are SFRs and can be accessed via direct addressing; mixing up source/destination order in MOV.

Final Answer:
MOV R2, P3