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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