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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode IN</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="IMUL.htm"> IMUL Signed Multiply</A><BR><B>next:</B><A HREF="INC.htm"> INC Increment by 1</A><P><HR><P><H1>IN -- Input from Port</H1><PRE>Opcode Instruction Clocks DescriptionE4 ib IN AL,imm8 12,pm=6*/26** Input byte from immediate port into ALE5 ib IN AX,imm8 12,pm=6*/26** Input word from immediate port into AXE5 ib IN EAX,imm8 12,pm=6*/26** Input dword from immediate port into EAXEC IN AL,DX 13,pm=7*/27** Input byte from port DX into ALED IN AX,DX 13,pm=7*/27** Input word from port DX into AXED IN EAX,DX 13,pm=7*/27** Input dword from port DX into EAX</PRE><EM><H3>Notes</H3><PRE> *If CPL <= IOPL **If CPL > IOPL or if in virtual 8086 mode</PRE></EM><H2>Operation</H2><PRE>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 *)</PRE><H2>Description</H2>IN transfers a data byte or data word from the port numbered by thesecond operand into the register (AL, AX, or EAX) specified by the firstoperand. Access any port from 0 to 65535 by placing the port numberin the DX register and using an IN instruction with DX as the secondparameter. These I/O instructions can be shortened by using an 8-bitport I/O in the instruction. The upper eight bits of the port address willbe 0 when 8-bit port I/O is used.<H2>Flags Affected</H2>None<H2>Protected Mode Exceptions</H2>#GP(0) if the current privilege level is larger (has less privilege) thanIOPL and any of the corresponding I/O permission bits in TSS equals 1<H2>Real Address Mode Exceptions</H2>None<H2>Virtual 8086 Mode Exceptions</H2>#GP(0) fault if any of the corresponding I/O permission bits in TSSequals 1<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="IMUL.htm"> IMUL Signed Multiply</A><BR><B>next:</B><A HREF="INC.htm"> INC Increment by 1</A></BODY>⌨️ 快捷键说明
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