IN -- Input from Port

IN -- Input from Port Opcode Instruction Clocks Description E4 ib IN AL,imm8 12,pm=6*/26** Input byte from immediate port into AL E5 ib IN AX,imm8 12,pm=6*/26** Input word from immediate port into AX E5 ib IN EAX,imm8 12,pm=6*/26** Input dword from immediate port into EAX EC IN AL,DX 13,pm=7*/27** Input byte from port DX into AL ED IN AX,DX 13,pm=7*/27** Input word from port DX into AX ED IN EAX,DX 13,pm=7*/27** Input dword from port DX into EAX --------------------------------------------------------------------------- NOTES: *If CPL <= IOPL **If CPL > IOPL or if in virtual 8086 mode --------------------------------------------------------------------------- Operation IF (PE = 1) AND ((VM = 1) OR (CPL > IOPL)) THEN (* Virtual 8086 mode, or protected mode with CPL > IOPL *) IF NOT I-O-Permission (SRC, width(SRC)) THEN #GP(0); FI; FI; DEST = [SRC]; (* Reads from I/O address space *) Description IN transfers a data byte or data word from the port numbered by the second operand into the register (AL, AX, or EAX) specified by the first operand. Access any port from 0 to 65535 by placing the port number in the DX register and using an IN instruction with DX as the second parameter. These I/O instructions can be shortened by using an 8-bit port I/O in the instruction. The upper eight bits of the port address will be 0 when 8-bit port I/O is used. Flags Affected None Protected Mode Exceptions #GP(0) if the current privilege level is larger (has less privilege) than IOPL and any of the corresponding I/O permission bits in TSS equals 1 Real Address Mode Exceptions None Virtual 8086 Mode Exceptions #GP(0) fault if any of the corresponding I/O permission bits in TSS equals 1