INC

Basic Info
Addressing Mode	Opcode	Length	Speed
Accumulator	1A	1 byte	2 cycles
Absolute	EE	3 bytes	6 cycles*
Direct Page	E6	2 bytes	5 cycles*
Absolute Indexed by X	FE	3 bytes	7 cycles*
Direct Page Indexed by X	F6	2 bytes	6 cycles*

Flags Affected
N	V	M	X	D	I	Z	C
N	.	.	.	.	.	Z	.

INC (Increment) is a 65x instruction that increments the value in the location specified 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 "INA."

INC ignores the decimal mode flag and the carry flag.

Syntax

INC
INC A
INA
INC addr
INC dp
INC addr, X
INC dp, X

To test for wraparound, examine the zero flag. If you need to add two or more to the accumulator, consider ADC instead of INC.

Cycle Penalties

• Except in accumulator addressing, INC takes two extra cycles when the accumulator is 16 bits wide.
• In direct page addressing modes, INC takes an extra cycle if the low byte of the direct page register is nonzero.

See Also

• INX
• INY
• DEC
• INC (SPC700)
• INC (Super FX)

External Links

• Eyes & Lichty, page 456 on INC
• Labiak, page 142 on INC
• 10.7 on MCS6500 Manual, page 155 on INC
• Carr, page 260 on INC
• Leventhal page 3-65 on INC: https://archive.org/details/6502-assembly-language-programming/page/n114
• snes9x implementation of INC: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L627
• undisbeliever on INC: https://undisbeliever.net/snesdev/65816-opcodes.html#inc-increment
• Pickens, John. http://www.6502.org/tutorials/6502opcodes.html#INC
• Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.1.1.3