Zilog Z80380 - Manual (Page 78)

5-44
Z380 ™
U SER ' S M ANUAL
DC-8297-03
Z ILOG
DEC
DECREMENT (BYTE)
DEC dst dst = R, RX, IR, X
Operation: dst
←
dst – 1
The destination operand is decremented by one and the result is stored in the destination.
Two’s complement subtraction is performed.
Flags: S: Set if the result is negative; cleared otherwise
Z: Set if the result is zero; cleared otherwise
H: Set if there is a borrow from bit 4 of the result; cleared otherwise
V: Set if arithmetic overflow occurs, that is, if the destination was 80H; cleared otherwise
N: Set
C: Unaffected
Addressing Execute
Mode Syntax Instruction Format Time Note
R: DEC R 00-r-101 note
RX: DEC RX 11y11101 0010w101 2
IR: DEC (HL) 00110101 2+r+w
X: DEC (XY+d) 11y11101 00110101 ——d— 4+r+w I
Field Encodings: r: per convention
y: 0 for IX, 1 for IY
w: 0 for high byte, 1 for low byte
Note: 2 for accumulator, 3 for any other register