SBC

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
		.	.	.	.

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.

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

• ADC
• SBC (SPC700)
• SUB (Super FX)

External Links

• Eyes & Lichty page 497, on SBC: https://archive.org/details/0893037893ProgrammingThe65816/page/497
• Labiak page 179 on SBC: https://archive.org/details/Programming_the_65816/page/n189
• MCS6500 Manual page 14 on SBC: https://archive.org/details/mos_microcomputers_programming_manual/page/n29
• Carr page 271 on SBC: https://archive.org/details/6502UsersManual/page/n284
• Leventhal page 3-91 on SBC: https://archive.org/details/6502-assembly-language-programming/page/n140
• snes9x implementation of SBC: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L1133
• undisbeliever on SBC: https://undisbeliever.net/snesdev/65816-opcodes.html#sbc-subtract-with-borrow-from-accumulator
• Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#SBC