ADC Add With Carry

Adds the data in the operand with the contents of the accumulator. Add 1 to the result if the carry flag is set. Store the final result in the accumulator.

Binary/Decimal mode

If the d flag is clear then binary addition is performed. If the d flag set then Binary Coded Decimal (BCD) addition is performed.

Data size

On all processors, the data added from memory is 8-bit. However, for 16-bit processors with the m flag is clear then the data added is 16-bit with the low-order 8-bits at the effective address and the high-order 8-bits at the effective address plus one.

Multi-precision arithmetic

In multi-precision (multi-word) arithmetic, the carry flag should be cleared before the low-order words are added. The addition will generate a new carry flag value based on that addition which will then be passed on to the next word.

For example, to add 1 to a 16-bit value at &70 on 8-bit processors:

1  CLC      ; Clear carry before first addition
2  LDA &70  ; Add 1 to low-order byte
3  ADC #1
4  STA &70
5  LDA &71  ; Add 0 to high order byte
6  ADC #0   ; This will add 1 if carry was set
7  STA &71  ; in the low-order byte

Flags Affected

Flags

Set if most-significant bit of result is set

Set if signed overflow

Set if result is zero

Set if unsigned overflow, clear if valid unsigned result

Instructions

Syntax	Opcode	Available on:			# of	# of	Addressing Mode
Syntax	(hex)	6502	65C02	65816	bytes	cycles	Addressing Mode
ADC #const	69	x	x	x	2¹	2^{2, 5}	Immediate
ADC addr	6D	x	x	x	3	4^{2, 5}	Absolute
ADC long	6F			x	4	5^{2, 5}	Absolute Long
ADC dp	65	x	x	x	2	3^{2, 3, 5}	Direct Page
ADC (dp)	72		x	x	2	5^{2, 3, 5}	Direct Page Indirect
ADC [dp]	67			x	2	6^{2, 3, 5}	Direct Page Indirect Long
ADC addr,X	7D	x	x	x	3	4^{2, 4, 5}	Absolute Indexed X
ADC long,X	7F			x	4	5^{2, 5}	Absolute Long Indexed X
ADC addr,Y	79	x	x	x	3	4^{2, 4, 5}	Absolute Indexed Y
ADC dp,X	75	x	x	x	2	4^{2, 3, 5}	Direct Page Indexed X
ADC (dp,X)	61	x	x	x	2	6^{2, 3, 5}	Direct Page Indexed Indirect X
ADC (dp),Y	71	x	x	x	2	5^{2, 3, 4, 5}	Direct Page Indirect Indexed Y
ADC [dp],Y	77			x	2	6^{2, 3, 5}	Direct Page Indirect Long Indexed Y
ADC sr,S	63			x	2	4^{2, 5}	Stack Relative
ADC (sr,S),Y	73			x	2	7^{2, 5}	Stack Relative Indirect Indexed Y

Notes:

65816: Add 1 byte if m=0 (16-bit memory/accumulator)
65816: Add 1 cycle if m=0 (16-bit memory/accumulator)
65816: Add 1 cycle if low byte of Direct Page register is not 0
Add 1 cycle if adding index crosses a page boundary
65C02: Add 1 cycle if d=1