qa.hlp (Table of Contents; Topic list)
Int 21H Function 04H
   Summary  Notes  Back
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  Description:  Auxiliary Output
 
  Outputs a character to the standard auxiliary device. The default is
  the first serial port (COM1).:
 
  Input                               Output
  ════════════════════════            ═══════
  AH=04H                              Nothing
  DL=8-bit data for output
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