Peripherally relevant to the recent discussion about accurate wristwatches I want to point out an interesting chip: Dallas/Maxim DS3231
This is a CMOS clock with built in 32.768 kHz X-tal and a couple of neat tricks: Every 64 seconds, it measures the temperature, and adjust the capacitive loading of the X-tal to match. They claim: (http://www.maxim-ic.com/datasheet/index.mvp/id/4627) # Accuracy ±2ppm from 0°C to +40°C # Accuracy ±3.5ppm from -40°C to +85°C And so far I have no reason to doubt them. That is not half bad, for a chip which can run for a week on a 1F super-capacitor... But, the _really_ neat thing is that it has an "Xtal aging" register, where the capacitive loading can be tuned, obviously necessary in the absense of an external trimmer. A quick test indicates that this happens in steps of roughly 0.05PPM Highly recommended... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
