User's Manual

THE 80286 INSTRUCTION SET
STOS/STOSB/STOSW-Store String Data
Opcode
AA
AS
AA
AS
FLAGS MODIFIED
None
Instruction
STOS mb
STOS mw
STOSS
STOSW
FLAGS UNDEFINED
None
OPERATION
Clocks
3
3
3
3
Description
Store AL to byte ES:[OI], advance 01
Store AX to word ES:[OI], advance 01
Store AL to byte ES:[OI], advance 01
Store AX to word ES:[OI], advance 01
STOS transfers the contents the AL or AX register to the memory byte or word at ES:DI. The operand
must be addressable from the
ES register; no segment override is possible.
After the transfer
is made, DI is automatically advanced. If the direction flag is 0 (CLD was executed),
DI increments;
if the direction flag is 1 (STD was executed), DI decrements. DI increments or decre-
ments
by 1 if a byte was moved; by 2 if a word was moved.
STOS can be preceded by the REP prefix for a block fill of CX bytes or words. Refer to the REP
instruction for details of this operation.
PROTECTED MODE EXCEPTIONS
#GP(O) if the destination is in a non-writable segment. #GP(O) for an illegal memory operand effective
address in the
CS, DS, or ES segments; #SS(O) for an illegal address in the SS segment.
REAL ADDRESS MODE EXCEPTIONS
Interrupt 13 for a word operand at offset OFFFFH.
S-107