Hello, Ausman, thank you for your input, In fact, I have never faced such an issue with HSC values. My HSC values never have been lost on the next day.
My task actually is to reset the HSC accumulated on previous day value once only - at the start of the machine next day. As Flex727 has advised, RTC SI and SB2 can be used for this purpose, and I use SI 37 , its value is incremented with 1 and stored to MI, so at the next power up, if it happens on the next day, that accumulated HSC value is reset. It works. Of course, now I have to implement mechanism to correct the MI value depending on what current month is. It needs some work, but as Flex727, nothing difficult. If you have brighter ideas how to do that, please advise. Thanks a lot!
P.S. To reset only once (first startup in the morning), I will use increment flag, so in case the machine has been restarted during the day (which happens couple of times actually), I will check that flag value, if it is different from 0, HSC will not be reset.