INT 14 - BIOS Asynchronous Communications Services

 	For more information, see the following topics:

	INT 14,0  Initialize serial port parameters
	INT 14,1  Send character in AL
	INT 14,2  Receive character in AL
	INT 14,3  Get Serial port status
	INT 14,4  Extended initialize  (PS/2)
	INT 14,5  Extended communication port control (PS/2)


	- all functions have:
	  AH = function number
	  AL = character to send or receive
	  DX = zero based RS232 card number
	- all registers are preserved except AX
	- these functions use hardware flow control
	- used by DOS MODE to redirect LPTx output to a serial device
	- see individual functions for more data


BIOS Asynchronous Communications Services (Status)

		│7│6│5│4│3│2│1│0│  AL  modem status
		 │ │ │ │ │ │ │ └──── clear to send status changed
		 │ │ │ │ │ │ └───── data set ready status changed
		 │ │ │ │ │ └────── trailing edge ring indicator
		 │ │ │ │ └─────── receive line signal changed
		 │ │ │ └──────── clear to send
		 │ │ └───────── data set ready
		 │ └────────── ring indicator
		 └─────────── receive line signal detected

		│7│6│5│4│3│2│1│0│  AH  port status
		 │ │ │ │ │ │ │ └──── data ready
		 │ │ │ │ │ │ └───── overrun error
		 │ │ │ │ │ └────── parity error
		 │ │ │ │ └─────── framing error
		 │ │ │ └──────── break detect
		 │ │ └───────── transmit holding register empty
		 │ └────────── transmit shift register empty
		 └─────────── time out (N/A for functions 1 and 2)