THE
80286
INSTRUCTION
SET
IN-Input
from
Port
Opcode Instruction
E4
db
IN
AL,db
EC
IN
AL,OX
E5
db
IN
AX,db
ED
IN
AX,OX
FLAGS MODIFIED
None
FLAGS UNDEFINED
None
OPERATION
ClockS
5
5
5
5
Description
Input
byte from immediate port into AL
Input byte from port
OX
into
AL
Input word from immediate port into AX
Input word from port
OX
into AX
IN
transfers a data byte or data word from the port numbered
by
the
second operand into the register
(AL or AX) given
as
the first operand. You can access any port from 0
to
65535
by
placing the port
number in the DX register then using an
IN
instruction with
DXas
the second parameter. These
I/O
instructions can be shortened by using an 8-bit port
I/O
in
the instruction. The upper 8 bits of the port
address
will
be zero when
an
8-bitport
I/Ois
used.
Intel has reserved
I/O
port addresses
OOF8H
through
OOFFH;
they should not be used.
PROTECTED MODE EXCEPTIONS
#GP(O)
if the current privilege level
is
bigger (has
less
privilege) than IOPL; which
is
the privilege
level found in the flags register.
REAL ADDRESS MODE EXCEPTIONS
None
8-45
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