INC

INC (short for "INCrease") is the mnemonic for a machine language instruction which increases the numerical value of the contents of the address specified by one, and "wraps over" when the numerical limits of a byte are exceeded.

• If the byte in question is taken as an unsigned integer, INC "counts" from 0 thru 255/$0 thru $FF. If a byte already containing the value 255/$FF is INCremented, it "wraps over" to the value 0.
• If the byte is taken as a signed integer, INC will "count" from −128 thru +127, or −$80 thru +$7F. If a byte already holding the value 127/$7F is INCremented, it "wraps over" to the value −128/−$80.

Addressing modes

Opcode		Addressing mode	Assembler format	Length in bytes	Number of cycles
Dec	Hex
238	EE	Absolute	INC nnnn	3	6
254	FE	Absolute,X	INC nnnn,X	3	7
230	E6	Zeropage	INC nn	2	5
246	F6	Zeropage,X	INC nn,X	2	6

INC supports the four different addressing modes shown in the table at right. In the assembler formats listed, nn represents a single-byte (8-bit) figure, and nnnn is a two-byte (16-bit) address.

CPU flags

INC affects 2 of the CPU's status flags:

• The negative status flag is set if the result is negative, i.e. has its most significant bit set.
• The zero flag is set if the result is zero, or cleared if it is non-zero.