i386/i386.reference/IN.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode IN</TITLE>
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  14 <H1>IN -- Input from Port</H1>
  15
  16 <PRE>
  17 Opcode    Instruction   Clocks            Description
  18
  19 E4  ib    IN AL,imm8    12,pm=6*/26**     Input byte from immediate port
  20                                           into AL
  21 E5  ib    IN AX,imm8    12,pm=6*/26**     Input word from immediate port
  22                                           into AX
  23 E5  ib    IN EAX,imm8   12,pm=6*/26**     Input dword from immediate port
  24                                           into EAX
  25 EC        IN AL,DX      13,pm=7*/27**     Input byte from port DX into AL
  26 ED        IN AX,DX      13,pm=7*/27**     Input word from port DX into AX
  27 ED        IN EAX,DX     13,pm=7*/27**     Input dword from port DX into
  28                                           EAX
  29 </PRE>
  30
  31 <EM>
  32 <H3>Notes</H3>
  33 <PRE>
  34    *If CPL <= IOPL
  35   **If CPL > IOPL or if in virtual 8086 mode
  36 </PRE>
  37 </EM>
  38
  39 <H2>Operation</H2>
  40
  41 <PRE>
  42 IF (PE = 1) AND ((VM = 1) OR (CPL > IOPL))
  43 THEN (* Virtual 8086 mode, or protected mode with CPL > IOPL *)
  44    IF NOT I-O-Permission (SRC, width(SRC))
  45    THEN #GP(0);
  46    FI;
  47 FI;
  48 DEST := [SRC]; (* Reads from I/O address space *)
  49 </PRE>
  50
  51 <H2>Description</H2>
  52
  53 IN transfers a data byte or data word from the port numbered by the
  54 second operand into the register (AL, AX, or EAX) specified by the first
  55 operand. Access any port from 0 to 65535 by placing the port number
  56 in the DX register and using an IN instruction with DX as the second
  57 parameter. These I/O instructions can be shortened by using an 8-bit
  58 port I/O in the instruction. The upper eight bits of the port address will
  59 be 0 when 8-bit port I/O is used.
  60
  61 <H2>Flags Affected</H2>
  62
  63 None
  64
  65 <H2>Protected Mode Exceptions</H2>
  66
  67 #GP(0) if the current privilege level is larger (has less privilege) than
  68 IOPL and any of the corresponding I/O permission bits in TSS equals 1
  69
  70 <H2>Real Address Mode Exceptions</H2>
  71
  72 None
  73
  74 <H2>Virtual 8086 Mode Exceptions</H2>
  75
  76 #GP(0) fault if any of the corresponding I/O permission bits in TSS
  77 equals 1
  78
  79
  80 <P>
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  82 <P>
  83 <B>up:</B> <A HREF="c17.htm">
  84 Chapter 17 -- 80386 Instruction Set</A><BR>
  85 <B>prev:</B><A HREF="IMUL.htm"> IMUL Signed Multiply</A><BR>
  86 <B>next:</B><A HREF="INC.htm"> INC Increment by 1</A>
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