INT 21 - DOS 1+ - WRITE CHARACTER TO STDAUX
AH = 04h
DL = character to write
Notes:  keyboard checked for ^C/^Break, 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
SeeAlso: INT 14/AH=01h,INT E0/CL=04h

See also: 2103

2104 - DOS 1+ - WRITE CHARACTER TO STDAUX