mirror of https://github.com/mre/mos6502.git
75 lines
1.1 KiB
Org Mode
75 lines
1.1 KiB
Org Mode
* 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
|
|
|