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SBC: Difference between revisions

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Revision as of 06:15, 25 July 2024

Basic Info
Addressing Mode Opcode Length Speed
Immediate E9 2/3 bytes 2 cycles*
Absolute ED 3 bytes 4 cycles*
Absolute Long EF 4 bytes 5 cycles*
Direct Page E5 2 bytes 3 cycles*
Direct Page Indirect F2 2 bytes 5 cycles*
Direct Page Indirect Long E7 2 bytes 6 cycles*
Absolute Indexed by X FD 3 bytes 4 cycles*
Absolute Long Indexed by X FF 4 bytes 5 cycles*
Absolute Indexed by Y F9 3 bytes 4 cycles*
Direct Page Indexed by X F5 2 bytes 4 cycles*
Direct Page Indexed Indirect by X E1 2 bytes 6 cycles*
Direct Page Indirect Indexed by Y F1 2 bytes 5 cycles*
Direct Page Indirect Long Indexed by Y F7 2 bytes 6 cycles*
Stack Relative E3 2 bytes 4 cycles*
Stack Relative Indirect Indexed by Y F3 2 bytes 7 cycles*
Flags Affected
N V M X D I Z C
N V . . . . Z C

SBC (Subtract with Carry/Borrow) is 65x instruction that performs a subtraction. The accumulator serves as the minuend. The operand serves as the subtrahend.

If the carry flag (aka borrow flag) is clear, one more is subtracted.

The difference is stored in the accumulator. If the difference is less than zero, the carry flag will be cleared and set otherwise.

Syntax

SBC #const
SBC addr
SBC long
SBC dp
SBC (dp)
SBC [dp]
SBC addr, X
SBC long, X
SBC addr, Y
SBC dp, X
SBC (dp, X)
SBC (dp), Y
SBC [dp], Y
SBC sr, S
SBC (sr, S), Y

Cycle Penalties

SBC 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

Retrieved from "https://sneslab.net/mw/index.php?title=SBC&oldid=19045"