2.2.25 (1) DEC (B)
DEC (DECrement)
Decrement
Operation
Rd – 1
→
Rd
Assembly-Language Format
DEC.B
Rd
Operand Size
Byte
Condition Code
H: Previous value remains unchanged.
N: Set to 1 if the result is negative; otherwise
cleared to 0.
Z:
Set to 1 if the result is zero; otherwise
cleared to 0.
V: Set to 1 if an overflow occurs (the
previous value in Rd was H'80);
otherwise cleared to 0.
C: Previous value remains unchanged.
I
UI
H
U
N
Z
V
C
—
—
—
—
↕
↕
↕
—
Description
This instruction decrements an 8-bit register Rd (destination register) and stores the result in the
8-bit register Rd.
Available Registers
Rd: R0L to R7L, R0H to R7H
Operand Format and Number of States Required for Execution
Notes
An overflow is caused by the operation H'80 – 1
→
H'7F.
Instruction Format
1st byte
2nd byte
3rd byte
4th byte
Register direct
DEC.B
Rd
1
A
0
rd
2
No. of
States
Addressing
Mode
Mnemonic
Operands
79