IN - Input Byte or Word From Port Usage: IN accum,port Modifies flags: None A byte, word or dword is read from port and placed in AL, AX or EAX respectively. If the port number is in the range of 0-255 it can be specified as an immediate, otherwise the port number must be specified in DX. Valid port ranges on the PC are 0-1024, though values through 65535 may be specified and recognized by third party vendors and PS/2's. Clocks Size Operands 808x 286 386 486 Bytes accum,immed8 10/14 5 12 14 2 accum,immed8 (PM) 6/26 8/28/27 2 accum,DX 8/12 5 13 14 1 accum,DX (PM) 7/27 8/28/27 1 - 386+ protected mode timings depend on privilege levels. first number is the timing if: CPL ó IOPL second number is the timing if: CPL > IOPL or in VM 86 mode (386) CPL ò IOPL (486) third number is the timing when: virtual mode on 486 processor - 486 virtual mode always requires 27 cycles
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