Intel 80286, 80287 manual IN-Input from Port

THE 80286 INSTRUCTION SET

IN-Input from Port

Opcode		Instruction	ClockS	Description
E4	db	IN AL,db	5	Input byte from immediate port into AL
EC		IN AL,OX	5	Input byte from port OX into AL
E5	db	IN AX,db	5	Input word from immediate port into AX
ED		IN AX,OX	5	Input word from port OX into AX

FLAGS MODIFIED

None

FLAGS UNDEFINED

None

OPERATION

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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