User's Manual

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
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