INT 70 - Real Time Clock Interrupt (XT 286,AT,PS/2)

	- called 1024 times per second for periodic and alarm functions
	- decrements a DWORD counter by 976µ sec (1/1024)
	- when DWORD reaches zero, bit 7 of designated wait flag is set
	- if alarm was enabled by  INT 1A,6,  INT 4A is called when
	  counter reaches zero to activate alarm handler
	- not available in model 30 PS/2

	- see	INT 15,83   INT 15,86