DOS

Herbert Kleebauer

2012-05-10 15:19:59 UTC

aaa

Bad command or file name

AAA -- ASCII Adjust after Addition

Opcode Instruction Clocks Description

37 AAA 4 ASCII adjust AL after addition

Operation

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

Description

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

None

Real Address Mode Exceptions

None

Virtual 8086 Mode Exceptions

None