Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 21h Function 03h
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  Interrupt:   21h     Function:   03h
 
  Title:       Auxiliary Input
 
  See also:    Read Character from Communications Port, Auxiliary Output
 
  Description:
 
     Reads a character from the standard auxiliary device. The default
     is the first serial port (COM1).
 
     Input        Output
 
     AH = 03h     AL = 8-bit input data
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