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DEC
DECREMENT
DEC
Operation:
(DEST)
+-
(DEST)-1
Flags
Affected:
Description:
DEC (Decrement) subtracts one from the
destination operand. The operand may
be a
byte or a word and
is
treated as an unsigned
binary number (see AAA and DAA). DEC
updates AF,
OF, PF, SF and ZF; it does not
affect CF.
Encoding:
Memory
or
Register Operand:
11111
11 1 w 1 mod 001 rIm 1
DEST=
EA
16-Bit Register Operand:
1
01
001
reg
DEST=
REG
AF,
OF,
PF, SF,
ZF
DEC
Operands
Clocks*
Transfers
Bytes
DEC Coding Example
reg16 2
- 1
DECAX
reg8
3
- 2
DECAL
memory 15(23)+
EA
2
2-4
DEC
ARRAY [SI]
*b(w): where b
denotes
the
number
of
clock
cycles
for
byte operands and
w
denotes
the
number
of
clock
cycles
for
word operands.
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