Int 21 Fn 04  - Dos 1+ - Write Character To Stdaux                         [D]

   AH = 04h
   DL = character to write

Notes: keyboard checked for ^C/reak, and INT 23 executed if detected
   STDAUX is usually the first serial port
   if STDAUX is busy, this function will wait until it becomes free

See Also: AH=03h,INT 14/AH=01h,INT E0/CL=04h