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Card #c521IR // #c521Synthesis

Internal RAM is stratified by function: 00H-1FH holds four banks of eight registers selected by RS1/RS0 (PSW.4/PSW.3), 20H-2FH gives 128 individually addressable bits, 30H-7FH is plain scratchpad — and the special-function registers sit in a separate control plane at 80H-FFH, addressable by name or number. The stack pointer starts at 07H, so the first push lands at 08H.

— In our words · Source: 8051 Microcontroller Notes

[Use when]

Writing or debugging 8051 code — choose register banks vs scratchpad deliberately, guard the stack against the register area, and reach control hardware only through its SFR addresses.

[Why it matters]

On the 8051, where data lives determines how you touch it — register bits, bit RAM, and SFRs each have their own access rules — so the memory map is not background detail, it is the instruction set's context.

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