PIC and RTC DS1307 problem - hardware vs software ?

[jorge]

I had this issue long ago with many DS1307's. I found a Dallas app note that suggests a large negative going spike on the supply rail will corrupt the clock. I verified with a scope that upon power up my supply was indeed going negative by five or ten volts. I put a shottky across the 5 volt line to clamp the negative spike and have not had a re occurrence of the corruption in many years. See the last page of the attached app note.

Thanks a lot Steve_88 !. I will try it.
I never thought of that because i have a power supply with a transformer with 12v and 9v regulators for relays and other electronics and only after i have another interconnected board with 7805 regulator powering the PIC , MAX 232 , RTC and so on ...also i ve smd BAS19 diodes protecting eveything for wrong assembling.
Since i ve no communications with an external PC or similar , i didn’t realize i could be getting negative spikes

by the way, where did you put the shottky precisely ? ...I am afraid about the ~0.3 voltage drop i will be getting from it in some components.

Thanks !!!