DEC 8-bit Decrement
Decrement
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
|---|---|---|---|---|---|---|---|---|
| \(r \longleftarrow r - 1\) | ||||||||
| DEC r | ||||||||
| 0 | 0 | r | 1 | 0 | 1 | |||
| \((HL) \longleftarrow (HL) - 1\) | ||||||||
| DEC (HL) | ||||||||
| 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | |
| \((IX+d) \longleftarrow (IX+d) - 1\) | ||||||||
| DEC (IX+d) | ||||||||
| 1 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | DD |
| 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 35 |
| d | ||||||||
| \((IY+d) \longleftarrow (IY+d) - 1\) | ||||||||
| DEC (IY+d) | ||||||||
| 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | FD |
| 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 35 |
| d | ||||||||
| Register | r |
|---|---|
| B | 000 |
| C | 001 |
| D | 010 |
| E | 011 |
| H | 100 |
| L | 101 |
| A | 111 |
Flags Affected
| Flags |
| ||||||||
|---|---|---|---|---|---|---|---|---|---|
| s | set if result negative | ||||||||
| z | set if result is 0 | ||||||||
| h | set if borrow from bit 4 | ||||||||
| p/v | set if register was 0x80 before operation, reset otherwise |
Opcode Matrix
| A | B | C | D | E | H | L | (HL) | (IX+d) | (IY+d) | |
|---|---|---|---|---|---|---|---|---|---|---|
| Op |
DEC A
3D14 |
DEC B
0514 |
DEC C
0D14 |
DEC D
1514 |
DEC E
1D14 |
DEC H
2514 |
DEC L
2D14 |
DEC (HL)
35111 |
DEC (IX+d)
DD35nn323 |
DEC (IY+d)
FD35nn323 |
|
Instruction
Opcode hexSize bytesCycle count
| Register | Memory |
Last modified November 16, 2021: Add flags to math operations (63d34c2)