ADC: Difference between revisions
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'''ADC''' (Add with Carry) is 65x instruction | '''ADC''' (Add with Carry) is the main 65x addition instruction. The accumulator is always both one of the addends and where the sum is stored. The operand serves as the other addend. | ||
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. | |||
After ADC runs, the [[carry flag]] will indicate whether the addition caused an unsigned overflow (sum greater than $FF or $FFFF depending on how wide the accumulator is). 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 (with the sum being adjusted automatically), otherwise binary addition. | |||
==== Syntax ==== | |||
<pre> | |||
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 | |||
</pre> | |||
==== 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 | |||
If you only need to add one, consider [[INC]] instead. Unlike the 65c02, the 65c816 does not have a cycle penalty when adding in decimal mode. | |||
=== See Also === | === See Also === | ||
Line 111: | Line 145: | ||
* [[ADC (SPC700)]] | * [[ADC (SPC700)]] | ||
* [[ADC (Super FX)]] | * [[ADC (Super FX)]] | ||
* [[ADD (Super FX)]] | |||
* [[INX]] | |||
* [[INY]] | |||
=== External Links === | === External Links === | ||
* [[Eyes & Lichty]] | * [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/423 page 423] on ADC | ||
* [[Labiak]] | * [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n125 page 115] on ADC | ||
* [[MCS6500 Manual]] page on ADC | * 2.2.1 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n22 page 7] on ADC | ||
* [[Carr]] | * [https://archive.org/details/mos_microcomputers_programming_manual/page/n204 B-3], lbid. | ||
* [[Leventhal]] | * [[Carr]], [https://archive.org/details/6502UsersManual/page/n258 page 245] on ADC | ||
* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n87 page 3-38] on ADC | |||
* undisbeliever on ADC: https://undisbeliever.net/snesdev/65816-opcodes.html#adc-add-with-carry | * 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 | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:Group One Instructions]] | [[Category:Group One Instructions]] | ||
[[Category:Inherited from 6502]] | [[Category:Inherited from 6502]] |
Latest revision as of 17:09, 22 October 2024
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 the main 65x addition instruction. The accumulator is always both one of the addends and where the sum is stored. The operand serves as the other addend.
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.
After ADC runs, the carry flag will indicate whether the addition caused an unsigned overflow (sum greater than $FF or $FFFF depending on how wide the accumulator is). 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 (with the sum being adjusted automatically), 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
If you only need to add one, consider INC instead. Unlike the 65c02, the 65c816 does not have a cycle penalty when adding in decimal mode.
See Also
External Links
- Eyes & Lichty, page 423 on ADC
- Labiak, page 115 on ADC
- 2.2.1 on MCS6500 Manual, page 7 on ADC
- B-3, lbid.
- Carr, page 245 on ADC
- Leventhal, page 3-38 on ADC
- 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