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ADC
From SnesLab
Basic Info | |||||||
---|---|---|---|---|---|---|---|
Addressing Mode | Opcode | Length | Speed | ||||
Immediate | 69 | 2/3 bytes | 2 cycles* | ||||
Absolute | 6D | 3 bytes | 4 cycles* | ||||
Absolute Long | 6F | 4 bytes | 5 cycles* | ||||
Direct Page | 65 | 2 bytes | 3 cycles* | ||||
Direct Page Indirect | 72 | 2 bytes | 5 cycles* | ||||
Direct Page Indirect Long | 67 | 2 bytes | 6 cycles* | ||||
Absolute Indexed by X | 7D | 3 bytes | 4 cycles* | ||||
Absolute Long Indexed by X | 7F | 4 bytes | 5 cycles* | ||||
Absolute Indexed by Y | 79 | 3 bytes | 4 cycles* | ||||
Direct Page Indexed by X | 75 | 2 bytes | 4 cycles* | ||||
Direct Page Indexed Indirect by X | 61 | 2 bytes | 6 cycles* | ||||
Direct Page Indirect Indexed by Y | 71 | 2 bytes | 5 cycles* | ||||
Direct Page Indirect Long Indexed by Y | 77 | 2 bytes | 6 cycles* | ||||
Stack Relative | 63 | 2 bytes | 4 cycles* | ||||
Stack Relative Indirect Indexed by Y | 73 | 2 bytes | 7 cycles* |
Flags Affected | ||||||||
---|---|---|---|---|---|---|---|---|
N | V | M | X | D | I | Z | C | |
N | V | . | . | . | . | Z | C |
ADC (Add with Carry) is 65x instruction that performs an addition. As there is no add-without-carry instruction, a CLC should be run (or the carry flag otherwise ensured to be clear) before an ADC, or else the sum will be one greater than expected.
The accumulator is always both one of the addends and where the sum is stored.
After ADC runs, the carry flag will indicate whether the addition caused an unsigned overflow. The zero flag will be set if the sum is zero and cleared otherwise.
If the decimal flag is set, then binary coded decimal addition is performed, otherwise binary addition.
Syntax
ADC #const ADC addr ADC long ADC dp ADC (dp) ADC [dp] ADC addr, X ADC long, X ADC addr, Y ADC dp, X ADC (dp, X) ADC (dp), Y ADC [dp], Y ADC sr, S ADC (sr, S), Y
Cycle Penalties
ADC takes an extra cycle for each of the following:
- if the accumulator is 16 bits wide, in all addressing modes
- when utilizing the direct register, if the low byte of the direct register is nonzero
- in certain addressing modes if adding an index crosses a page boundary
See Also
External Links
- Eyes & Lichty, page 423 on ADC
- Labiak, page 115 on ADC
- MCS6500 Manual page 7 on ADC: https://archive.org/details/mos_microcomputers_programming_manual/page/n22
- https://archive.org/details/mos_microcomputers_programming_manual/page/n204, lbid.
- Carr page 245 on ADC: https://archive.org/details/6502UsersManual/page/n258
- Leventhal page 3-38 on ADC: https://archive.org/details/6502-assembly-language-programming/page/n87
- undisbeliever on ADC: https://undisbeliever.net/snesdev/65816-opcodes.html#adc-add-with-carry
- Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#ADC
- Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.1.1