IN

IN - Input Byte or Word From Port

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.

Usage:

	IN	accum,port	;

Modifies flags:

none

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 ¾ IOPL
second number is the timing if: CPL > IOPL or in VM 86 mode (386)
CPL ‗ IOPL (486)
third number is the timing when: virtual mode on 486 processor
  • 486 virtual mode always requires 27 cycles