INT 10 - VIDEO - SCREENR v1.55+ - API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes.
	AX = 5049h ('PI')
	BX = function
	    0000h installation check
	    0001h lock mode
	    0002h unlock mode
	    0003h lock palette
	    0004h unlock palette
Return: AX = 0000h if installed
	    BX = TSR(Terminate and Stay Resident) A program which remains in memory after terminating in order to provide services to other programs or the user.  The name comes from the name of the DOS function call used to remain in memory after termination. version (BH=major,BL=minor)
	    CL = mode locking status
		00h mode not locked
		01h mode locked: INT 10/AH=00h disabled
	    CH = palette locking status
		00h palette not locked
		01h palette locked, the following functions are disabled:
			AX=1000h, AX=1001h, AX=1002h, AX=1010h, AX=1012h
Program: SCREENR is a TSR(Terminate and Stay Resident) A program which remains in memory after terminating in order to provide services to other programs or the user.  The name comes from the name of the DOS function call used to remain in memory after termination. supplied with Patrick Ibbetson's SCREEN display
	  utility.
Index:	installation check;SCREENR