6502 Addressing Modes - Plus/4 Encyclopedia



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6502 Addressing Modes
Category Programming/Assembly Topic What are addressing modes? Most CPU instructions deal with the memory. When you access the memory, you can refer to it in various ways. For example, LDA $1021 would load memory location $1021 into the "A" register. Directly referring to memory location $1021 in this case is an example of "Absolute addressing mode". However, we could also use LDX #$21, LDA $1000,X. The ",X" part tells the CPU to look up the "X"th ($21th in this case) memory address from $1000. So esentially this example also reads the same memory location, but we've used "Absolute,X addressing mode". The 6502 has the following 13 addressing modes: Implicit addressing mode Accumulator addressing mode Immediate addressing mode Zero Page addressing mode Zero Page,X addressing mode Zero Page,Y addressing mode Relative addressing mode Absolute addressing mode Absolute,X addressing mode Absolute,Y addressing mode Indirect addressing mode Indexed Indirect addressing mode Indirect Indexed addressing mode Keywords addressing modes