Expects: AH    01H
AL    byte to send
DX    COMM port number (0 to 3)
                                                                  
Returns: AH    bit 7=0 if no error;
else, bits 0-6 have Line Status see BIOS COM status codes
                                                                  
Info: Transmits the character in AL over the specified COM line.

Notes: The return status code cannot indicate a time out error, since
bit 7 is used to flag any error.  Thus, after any error, you
should use INT 14H 03H to get the full story on what went wrong.

- -

INT 14H 01H: Send a Character