5
The 68000's Instruction Set
Sample syntax: ADDQ #6,D3
Attributes: Size = byte, word, longword
Description: Add the immediate data to the contents of the destination operand.
The immediate data must be in the range 1 to 8. Word and
longword operations on address registers do not affect condition
codes. Note that a word operation on an address register affects
all bits of the register.
Application: ADDQ is used to add a small constant to the operand at the effective
address. Some assemblers permit you to write ADD and then choose
ADDQ automatically if the constant is in the range 1 to 8.
Condition codes: Z N Z V C
* * * * *
Note that the CCR is not updated if the destination operand is an
address register.
Destination operand addressing modes
ADDX Add extended
Operation: [destination] ← [source] + [destination] + [X]
Syntax: ADDX Dy,Dx
ADDX -(Ay),-(Ax)
Attributes: Size = byte, word, longword
Description: Add the source operand to the destination operand along with
the extend bit, and store the result in the destination location.
The only legal addressing modes are data register direct and
memory to memory with address register indirect using pre-
decrementing.
Application: The ADDX instruction is used in chain arithmetic to add together
strings of bytes (words or longwords). Consider the addition of