
Z80 Instruction Set UM008007-0715
168
Z80 CPU
User Manual
DEC m
Operation
m ← m – 1
Op Code
DEC
Operand
m
The m operand is any of r, (HL), (IX+d), or (lY+d), as defined for the analogous INC
instructions. These possible op code/operand combinations are assembled as follows in
the object code:
r identifies registers B, C, D, E, H, L, or A assembled as follows in the object code field:
Register r
B 000
C 001
D 010
E 011
H 100
L 101
A 111
00 r 011
00 1 01110
35
11 1 01101
DD
00 1 01110
35
11 1 01111
FD
00 1 01110
35
DEC (HL)
DEC (IX+d)
DEC (IY+d)
d
d
DEC r*
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