Accuracy specs of the K64_120 on board RTC


Accuracy specs of the K64_120 on board RTC

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Contributor I

I can't seem to find any specs on the accuracy of the RTC built into the K64_120.  Is it 1 sec/year or 1 sec/day or somewhere in between.

If you know of a doc that can clue me in I would much appreciate.

Thanks for any info you can provide!


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Senior Contributor III

The K64 RTC is just a counter -- accuracy is entirely up to the crystal specs and as tuned with the onchip caps.  I get about 1sec/day (11.6ppm).  You can 'do better' compensating for TC, but 'only while the CPU is running' (say you wake up every hour and adjust the caps OR the 'compensation reg').  I don't use the compensation reg, mostly because I am extrapolating the prescaler counts to time 'tens of microseconds' at the lowest level, and that math requires 32768 counts per second.

My XTAL = Abracon ABS10-32.768KHZ-7-T    +/-20ppm, another 0 to -20ppm 10C to 50C

I set the chip caps to 8 pf.

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