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INSB      Input Byte String From Port (186/286/386)  Flags: O D I T S Z A P C

INSB

           Logic:          ES:DI . byte from source port
                           if DF = 0 then
                               DI . DI + 1
                           else
                               DI . DI - 1

     The INSB instruction lets you read a byte string from a port. The
     destination string is pointed to by ES:DI. The input port number must be
     in DX. If the direction flag is set, DI is decremented. If it is not set,
     DI is incremented.

  --------------------------------------------------------------------------
   Operands                   Clocks   Transfers  Bytes  Example
   INSB                       5 (286)      1        1    INSB
  --------------------------------------------------------------------------

        Note:          This instruction is usually used with a REP
                       prefix. Load CX with the number of times to repeat
                       the instruction.