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DAS -- Decimal Adjust AL after Subtraction

Opcode    Instruction        Clocks   Description

2F        DAS                4        Decimal adjust AL after subtraction

Operation

IF (AL AND 0FH) > 9 OR AF = 1
THEN
   AL := AL - 6;
   AF := 1;
ELSE
   AF := 0;
FI;
IF (AL > 9FH) OR (CF = 1)
THEN
   AL := AL - 60H;
   CF := 1;
ELSE CF := 0;
FI;

Description

Execute DAS only after a subtraction instruction that leaves a two-BCD-digit byte result in the AL register. The operands should consist of two packed BCD digits. DAS adjusts AL to contain the correct packed two-digit decimal result.

Flags Affected

AF and CF as described above; SF, ZF, and PF as described in Appendix C.

Protected Mode Exceptions

None

Real Address Mode Exceptions

None

Virtual 8086 Mode Exceptions

None

up: Chapter 17 -- 80386 Instruction Set
prev: DAA Decimal Adjust AL after Addition
next: DEC Decrement by 1