Zilog Z08470 User Manual
Page 181
UM008007-0715
Z80 Instruction Description
Z80 CPU
User Manual
169
Description
The byte specified by the m operand is decremented.
Condition Bits Affected
S is set if result is negative; otherwise, it is reset.
Z is set if result is 0; otherwise, it is reset.
H is set if borrow from bit 4, otherwise, it is reset.
P/V is set if m was
80h
before operation; otherwise, it is reset.
N is set.
C is not affected.
Example
If the D Register contains byte
2Ah
, then upon the execution of a DEC D instruction, the D
Register contains
29h
.
Instruction
M Cycles
T States
4 MHz E.T.
DEC r
1
4
1.00
DEC (HL)
3
11 (4, 4, 3)
2.75
DEC (IX+d)
6
23 (4, 4, 3, 5, 4, 3)
5.75
DEC (lY+d)
6
23 (4, 4, 3, 5, 4, 3)
5.75