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75 lines
1.1 KiB
Org Mode
75 lines
1.1 KiB
Org Mode
* Addressing modes
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has a 16-byte address bus.
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** Absolute
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- Full memory location specified, i.e. $c000
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- 65536 bytes of addressable memory (2^16 duyyy)
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** Zero-page
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- 1 byte adress, i.e. $c0, 256 bytes adressable
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- faster, takes less program space
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** Zero-page, X
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- Relative adressing _within_ the zero page.
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- Adds the value in reg. x with a 1-byte adress
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- i.e. STA $a0, X
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- Address wraps around if the addition is larger than 1 byte
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** Zero-page, Y
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- equiv to zero-page, X but can only be used with LDX and STX
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** Immediate
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- i.e. #$c0
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- loads immedate number into register
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** Relative
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- i.e. $c0, or label
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** Implicit
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- when operation doesn't deal with memory
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** Indirect
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- Uses absolute address to get another address
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- first address is LSB of address, following byte is MSB
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** Indexed Indirect
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- i.e. LDA ($c0, X)
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- Take a zero page adress and add the value in reg. x to it, look up 2 byte address
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** Indirect Indexed
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- zero page address dereferenced then Y is added to it
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* Stack
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- lives in memory between $0100 and $01ff
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* Jumping
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- JSR/RTS: Jump to subroutine and return from subroutine
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