INT 15 - SYSTEM - POINTING DEVICE BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware.  The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. INTERFACE (PSIBM PS/2, any model) - SET DEVICE HANDLER ADDR
	AX = C207h
	ES:BX -> FAR user device handler or 0000h:0000h to cancel
Return: CF set on error
	    AH = status (see #00522)
Note:	when the subroutine is called, it is passed the following values on
	  the stack; the handler should return with a FAR return without
	  popping the stack:
		WORD 1: status (see #00525)
		WORD 2: X data (high byte = 00h)
		WORD 3: Y data (high byte = 00h)
		WORD 4: 0000h
SeeAlso: INT 33/AX=000Ch


Bitfields for pointing device status:
Bit(s)	Description	(Table 00525)
 15-8	reserved (0)
 7	Y data overflowed
 6	X data overflowed
 5	Y data is negative
 4	X data is negative
 3	reserved (1)
 2	reserved (0)
 1	right button pressed
 0	left button pressed