Ascii Adjust for Subtraction
|
86/88 |
Y |
186 |
Y |
286 |
Y |
386 |
Y |
486 |
Y |
AAS |
|
Ovfl |
? |
Dir |
N |
Int |
N |
Trap |
N |
Sign |
? |
Zero |
? |
Aux |
Y |
Prty |
? |
Carry |
Y |
AAS corrects the result of a previous subtraction of two valid
unpacked BCD operands, changing the content of AL to a valid BCD
number. The destination operand of the subtraction must have been
specified as AL. The high-order nibble of AL is always set to 0.
Note: Unpacked BCD stores one digit per byte; AH contains
the most-significant digit and AL the least-
significant digit.
------------------------------------ Timing ----------------------------------
OpCode Instruction 386 286 86
3F AAS 4 3 8
------------------------------------ Logic -----------------------------------
If (AL & 0Fh) > 9 or AF = 1 then
AL = AL - 6
AH = AH - 1
AF = 1
CF = 1
else
AF = 0
CF = 0
AL = AL and 0Fh
See Also AAA AAD AAM SUB SBB DAA DAS DEC NEG Flags |