MSC: unsigned _bios_serialcom(unsigned cmd,unsigned port,unsigned fmt)

	- prototype in bios.h

	- cmd	= _COM_INIT	initialize port  (INT 14,0)
		= _COM_SEND	send character  (INT 14,1)
		= _COM_RECEIVE	read character from port  (INT 14,2)
		= _COM_STATUS	get serial port status  (INT 14,3)

	- fmt = combination of the following:
		_COM_CHR7	_COM_CHR8
		_COM_STOP1	_COM_STOP2

		_COM_NOPARITY	_COM_EVENPARITY	   _COM_ODDPARITY

		_COM_110	_COM_150	   _COM_300
		_COM_600	_COM_1200	   _COM_2400
		_COM_4800	_COM_9600

	- returns status word (INT 14, AX reg, modem status in AL,
	  port status in AH)
	- Turbo C uses bioscom()
	- see  INT 14