TC: int bioscom( int cmd, char byte, int port )

	- prototype in bios.h

	- RS232 communications

	- cmd = 0 to set comm parms to value in byte
		1 to send char in byte out on RS232 line
		2 to receive char
		3 to return current port status

	- port = 0 for COM1
		 1 for COM2
		 2 for COM3
		 3 for COM4

	- byte = bitwise OR of following bits
		 0x02 = 7 data bits    0x00 = 1 stop bit
		 0x03 = 8 data bits    0x04 = 2 stop bits
		 0x00 == no parity;
		 0x08 == odd parity;
		 0x18 == even parity

		 0x00	  110 bps	0x20	 150 bps
		 0x40	  300 bps	0x60	 600 bps
		 0x80	  1200 bps	0xa0	 2400 bps
		 0xc0	  4800 bps	0xe0	 9600 bps

	- returns 16-bit integer, upper 8 bits are status & lower 8 bits
	  depending on cmd sent


	│7│6│5│4│3│2│1│0│  low byte (AL)  modem status
	 │ │ │ │ │ │ │ └──── delta clear to send
	 │ │ │ │ │ │ └───── delta data set ready
	 │ │ │ │ │ └────── trailing edge ring detector
	 │ │ │ │ └─────── delta receive line signal detect
	 │ │ │ └──────── clear to send
	 │ │ └───────── data set ready
	 │ └────────── ring indicator
	 └─────────── receive line signal detect

	│F│E│D│C│B│A│9│8│  high byte (AH)  line status
	 │ │ │ │ │ │ │ └──── data ready
	 │ │ │ │ │ │ └───── overrun error
	 │ │ │ │ │ └────── parity error
	 │ │ │ │ └─────── framing error
	 │ │ │ └──────── break detect
	 │ │ └───────── transmit holding register empty
	 │ └────────── transmit shift register empty
	 └─────────── time out

	- MS C uses _bios_serialcom()
	- see  INT 14