Format of TI Professional PC timing event table:
Offset	Size	Description	)
 00h	WORD	offset of next event table entry
 02h	BYTE	normally unused (FFh)
 03h	BYTE	flags:
		bit 7 set if timing event active
		bits 6-0 not used by BIOS (0), but could be used by option ROMs
 04h	WORD	timeout count (decremented every 25ms when active)
 06h	WORD	offset of event handler (in segment F400h) to call on event
		  timeout; the F400h segment allows addressing both system ROMs
		  and the first 16K of memory (due to the 1M memory wraparound)