User's Manual

THE 80286 INSTRUCTION SET
DAS-Decimal Adjust AL After Subtraction
Opcode Instruction
Clocks
Description
2F DAS
3 Decimal adjust AL after subtraction
FLAGS MODIFIED
Sign, zero, auxiliary carry, parity, carry
FLAGS UNDEFINED
Overflow
OPERATION
DAS should be executed only after a subtraction instruction which leaves a two-BCD-digit byte result
in the AL register. The operands should consist of two packed BCD digits. In this case, the DAS
instruction will adjust AL to contain the correct packed two-digit decimal result.
The precise definition of
DAS is as follows:
1. If the lower four bits of AL are greater than 9, or if the auxiliary carry flag is 1, then decrement
AL by 6, and set the auxiliary carry flag. Otherwise, reset the auxiliary carry flag.
2. If AL is now greater than 9FH, or if the carry flag is set, then decrement 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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