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REAL - TIME CLOCKS Application Note 632: Aug 01, 2001

Evaluating the Accuracy of Maxim Real-Time Clocks (RTCs)
This app note describes methods for measuring the accuracy of the Maxim Real-Time
Clocks (RTCs) using available accurate time sources and the Maxim evaluation kits.

Evaluating the accuracy of Maxim real - time clocks (RTCs) can be simplified using the modern
personal computer (PC), an Internet connection, and RTC evaluation softwa re. Whether you
use a Maxim evaluation kit and its associated software to evaluate the accuracy of a Maxim
real - time clock, or use your own software and hardware configuration, you can take advantage
of the easy methods presented here for long - term accurac y testing of RTCs.
RTC Evaluation Software
Figure 1 shows the main screen of typical Maxim RTC evaluation software. The "offset 1 sec"
in the current - time display section of the screen is computed as offset = RTC time - PC time.
This is now an easy and con venient way to keep track of the difference between the RTC time
and PC time and thus allows for long - term accuracy testing of the RTC.
When reading the RTC, the timekeeping registers are latched during a burst read. Even though
the RTC evaluation softwar e reads the timekeeping registers approximately four times per
second, the best guaranteed resolution is 1 second, as all four reads could happen inside of a 1 -
second update. Therefore, an initial offset calculation of ±1 second is within the resolution of
the setup when testing for long - term RTC accuracy.
The only issue now is the accuracy of the standard that the RTC time is being compared
against, the PC clock.