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mre-mos6502/notes/6502Arch.org
Alex Weisberger db3ae89745 add org files
2014-10-07 23:51:30 -04:00

1.1 KiB

Addressing modes

has a 16-byte address bus.

Absolute

  • Full memory location specified, i.e. $c000
  • 65536 bytes of addressable memory (2^16 duyyy)

Zero-page

  • 1 byte adress, i.e. $c0, 256 bytes adressable
  • faster, takes less program space

Zero-page, X

  • Relative adressing within the zero page.
  • Adds the value in reg. x with a 1-byte adress
  • i.e. STA $a0, X
  • Address wraps around if the addition is larger than 1 byte

Zero-page, Y

  • equiv to zero-page, X but can only be used with LDX and STX

Immediate

  • i.e. #$c0
  • loads immedate number into register

Relative

  • i.e. $c0, or label

Implicit

  • when operation doesn't deal with memory

Indirect

  • Uses absolute address to get another address
  • first address is LSB of address, following byte is MSB

Indexed Indirect

  • i.e. LDA ($c0, X)
  • Take a zero page adress and add the value in reg. x to it, look up 2 byte address

Indirect Indexed

  • zero page address dereferenced then Y is added to it

Stack

  • lives in memory between $0100 and $01ff

Jumping

  • JSR/RTS: Jump to subroutine and return from subroutine