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DAA -- Decimal Adjust AL after Addition

Opcode    Instruction        Clocks   Description

27        DAA                4        Decimal adjust AL after addition

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

Flags Affected

AF and CF as described above; SF, ZF, PF, and CF 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: CWD/CDQ Convert Word to Doubleword/Convert Doubleword to Quadword
next: DAS Decimal Adjust AL after Subtraction