8051 memory transfer instructions Is it true that data transfer from I/O to external data memory can only be done with MOV?

Introduction / Context:
The 8051 has distinct instructions for internal data memory, external data memory, and code memory spaces. This question probes whether MOV is the only way to move data involving external data memory and I/O ports.

Given Data / Assumptions:

• MOV operates on internal RAM, SFRs, and port SFRs.
• MOVX is the dedicated instruction for external data memory (xdata).
• I/O ports are accessed via SFR addresses (for example, P0, P1, P2, P3).

Concept / Approach:
External data memory requires MOVX @DPTR, A or MOVX A, @DPTR (or @Ri). Data can be staged through A between port SFRs and external RAM using MOV and MOVX in sequence; therefore, MOV is not the only instruction involved when xdata is accessed.

Step-by-Step Solution:

Verification / Alternative check:
Consult any 8051 instruction set summary: MOVX is listed as the instruction for xdata; MOV accesses internal/SFR spaces.

Why Other Options Are Wrong:

• True: Incorrect because MOVX is required for external data memory.
• True, but only in mode 0 / EA LOW: Operating mode or EA pin does not change MOVX requirement for xdata.

Common Pitfalls:
Assuming MOV can directly access all spaces; on 8051, memory spaces are distinct and require the correct instruction.

Final Answer:
False — external data memory transfers use MOVX, often combined with MOV to/from ports.