User's Manual

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
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