80386 Programmer's Reference Manual -- Opcode AAA

AAA -- ASCII Adjust after Addition

OpcodeInstructionClocks DescriptionExample
37aaa 4 ASCII adjust AL after additionaaa


IF ((AL AND 0FH) > 9) OR (AF = 1)
   AL := (AL + 6) AND 0FH;
   AH := AH + 1;
   AF := 1;
   CF := 1;
   CF := 0;
   AF := 0;


Execute AAA only following an ADD instruction that leaves a byte result in the AL register. The lower nibbles of the operands of the ADD instruction should be in the range 0 through 9 (BCD digits). In this case, AAA adjusts AL to contain the correct decimal digit result. If the addition produced a decimal carry, the AH register is incremented, and the carry and auxiliary carry flags are set to 1. If there was no decimal carry, the carry and auxiliary flags are set to 0 and AH is unchanged. In either case, AL is left with its top nibble set to 0. To convert AL to an ASCII result, follow the AAA instruction with OR AL, 30H.

Flags Affected

AF and CF as described above; OF, SF, ZF, and PF are undefined

Protected Mode Exceptions


Real Address Mode Exceptions


[Home Page dell'ITIS "Fermi"] [80386 Programmer's Reference Manual Index] [Previous] [Next]