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THE
80286
INSTRUCTION SET
DAA-Decimal
Adjust
AL
After
Addition
Opcode Instruction Clocks Description
27
DAA
3
Decimal adjust
AL
after addition
FLAGS MODIFIED
Sign, zero, auxiliary carry, parity, carry
FLAGS UNDEFINED
Overflow
OPERATION
DAA
should be executed only after an ADD instruction which leaves a two-BCD-digit byte result in
the
AL
register. The ADD operands should consist of two packed BCD digits.
In
this case, the DAA
instruction will adjust
AL
to contain the correct two-digit packed decimal result.
The precise definition of DAA
is
as follows:
1.
If
the lower 4 bits of
~L
are greater than nine, or if the auxiliary carry flag
is
1,
then increment
AL
by 6, and set the)l.uxiliary carry flag. Otherwise, reset the auxiliary carry flag.
2.
I . .
If
AL
is now greater than 9FH, or
if
the carry flag
is
set, then increment
AL
by 60H, and set the
carry flag. Otherwise, clear the carry flag.
PROTECTED MODE EXCEPTIONS
None
REAL ADDRESS MODE EXCEPTIONS
None
8-36