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Card #c522IR // #c522Synthesis

The 8051 offers five addressing modes — immediate, register, direct, register-indirect, indexed — but register-indirect into internal RAM is limited to R0 and R1, and code-space table reads use MOVC A,@A+DPTR while external data uses MOVX; the chip keeps a 64 KB code space and a separate 64 KB external data space, so the instruction, not just the address, chooses which memory you touch.

— In our words · Source: 8051 Microcontroller Notes

[Use when]

Laying out data on an 8051 — put constant tables in code space for MOVC, variables in external data space for MOVX, and keep pointer discipline to R0/R1 for internal indirect access.

[Why it matters]

This is the notes' recurring lesson that addressing is a hardware data path, not just syntax: the same DPTR can reach ROM via MOVC or external RAM via MOVX, and that distinction is how lookup tables, external memory, and code fetches stay separate on a 16-bit address bus.

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