8051 external data memory access — is data transfer to/from external RAM possible only via the MOVX instruction? Evaluate whether external data memory reads/writes require MOVX (with DPTR or @R0/@R1 as pointer).

Introduction / Context:
The 8051 distinguishes among internal RAM, external data memory (often called XDATA), and code memory. Each space has specific instructions for access. Knowing which instruction accesses which space prevents illegal opcodes and logic errors.

Given Data / Assumptions:

• Target space: external data memory (XDATA)
• Candidate instructions: MOVX, MOV, MOVC
• Pointers: DPTR or @R0/@R1 for indirect external addressing

Concept / Approach:
External data memory is accessed exclusively with MOVX. MOVC reads code memory; MOV operates on internal RAM and SFRs. Therefore, any transfer to or from external data memory ultimately uses MOVX, typically via the Accumulator as the data register (A ← MOVX @DPTR or MOVX @DPTR, A). I/O port values can be staged through A but the external RAM write itself still uses MOVX.

Step-by-Step Solution:

Verification / Alternative check:
No legal MOV form targets XDATA; MOVC is code fetch only. Hence MOVX is required for external RAM access on classic 8051 devices.

Why Other Options Are Wrong:

• False: contradicts ISA rules.
• Only for reads/writes: MOVX is used for both directions.
• Port direct to XDATA: still requires staging and MOVX for the actual memory cycle.

Common Pitfalls:

• Confusing MOVC (code memory) with MOVX (external data memory).

Final Answer:
True