Int 14 Fn 21  - Multidos Plus - Transmit Character                         [S]

   AH = 21h
   AL = character to send
   DX = port number

Return: AH = status (see below)

Note:  monitor mode must have been turned on with AH=24h before calling

See Also: AH=20h"MultiDOS",AH=22h"MultiDOS",AH=24h"MultiDOS"

Values for status:
 00h   successful
 39h   no DSR or CTS
 3Ch   no DSR
 3Bh   no CTS
 41h   no such port
 42h   monitor mode not active
 97h   timed out