mre-mos6502/notes/6502Arch.org

• Addressing modes
  • Absolute
  • Zero-page
  • Zero-page, X
  • Zero-page, Y
  • Immediate
  • Relative
  • Implicit
  • Indirect
  • Indexed Indirect
  • Indirect Indexed
• Stack
• Jumping

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