mre-mos6502/notes/6502Arch.org

* 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