8051 indirect addressing semantics What does the instruction MOV A, @R1 do in the 8051?

Introduction / Context:Indirect addressing allows access to internal RAM using a register as a pointer. This question checks your understanding of the 8051 syntax @R1, which dereferences R1 to obtain the target byte.

Given Data / Assumptions:

• @R1 means “address contained in R1”.
• MOV A, @R1 reads from internal data memory at that address.
• R0 or R1 are valid indirect address registers in the 8051.

Concept / Approach:Dereferencing R1 provides a byte from internal data memory 0x00–0x7F (lower 128) or indirectly from 0x00–0xFF on variants; the byte is then moved into A. No flags are affected by the addressing mode itself.

Step-by-Step Solution:

Verification / Alternative check:Compare with MOV @R1, A which writes A to the addressed memory, confirming the direction of transfer is reversed in that form.

Why Other Options Are Wrong:

• Copy R1 to A: That would be MOV A, R1.
• Copy A to R1: That would be MOV R1, A.
• Copy A to memory at R1: That would be MOV @R1, A.

Common Pitfalls:Confusing register direct (R1) with register indirect (@R1) addressing, and mixing up source/destination order.

Final Answer:copy the contents of memory whose address is in R1 to the accumulator