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DEC: Difference between revisions

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(→‎External Links: hid archive URL for Carr)
(→‎External Links: hid archive URL for Leventhal)
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* 10.8 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n176 page 155] on DEC
* 10.8 on [[MCS6500 Manual]], [https://archive.org/details/mos_microcomputers_programming_manual/page/n176 page 155] on DEC
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n270 page 257] on DEC
* [[Carr]], [https://archive.org/details/6502UsersManual/page/n270 page 257] on DEC
* [[Leventhal]] page 3-60 on DEC: https://archive.org/details/6502-assembly-language-programming/page/n109
* [[Leventhal]], [https://archive.org/details/6502-assembly-language-programming/page/n109 page 3-60] on DEC
* snes9x implementation of DEC: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L482
* snes9x implementation of DEC: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L482
* undisbeliever on DEC: https://undisbeliever.net/snesdev/65816-opcodes.html#dec-decrement
* undisbeliever on DEC: https://undisbeliever.net/snesdev/65816-opcodes.html#dec-decrement

Revision as of 12:19, 8 August 2024

Basic Info
Addressing Mode Opcode Length Speed
Accumulator 3A 1 byte 2 cycles
Absolute CE 3 bytes 6 cycles*
Direct Page C6 2 bytes 5 cycles*
Absolute Indexed by X DE 3 bytes 7 cycles*
Direct Page Indexed by X D6 2 bytes 6 cycles*
Flags Affected
N V M X D I Z C
N . . . . . Z .

DEC (Decrement) is a 65x instruction that decrements the value in the location specified by the operand by one. The size of the accumulator determines whether this is an 8 or 16 bit operation. An alternate mnemonic when the operand is the accumulator is "DEA."

DEC ignores the decimal mode flag and the carry flag.

Syntax

DEC
DEC A
DEA
DEC addr
DEC dp
DEC addr, X
DEC dp, X

If you need to subtract two or more from the accumulator, consider SBC instead.

Cycle Penalties

See Also

External Links