Questions and discussions about the hardware aspects of the TD RF modules, boards and accessories.
ramon2015
 
Posts: 51
Joined: Mon Jul 06, 2015 4:06 pm

RTC accuracy

by ramon2015 Mon Nov 16, 2015 12:25 pm

Hello,

I am planing to use Real Time Clock (RTC) for my application and I have several questions:

- The XTAL 32Khz is the one used for Sleep Modes, right? so It is the one to use for periodic wake-ups, right?
- How accurate is the RTC?
- How often would i need to sync it via downlink message?

Regards, Ramon.
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mstempin
 
Posts: 168
Joined: Thu May 07, 2015 9:24 am

Re: RTC accuracy

by mstempin Tue Nov 17, 2015 3:07 pm

Hi Ramon,

The RTC is running at 32768 kHz on the internal Low-Frequency RC Oscillator (LFRCO), not on the "external" (well, inside the module!) Low-Frequency 32 kHz Crystal Oscillator (LFXO).

It is possible to calibrate the internal RC oscillator using the external crystal with the TD_RTC_CalibratedDelay() function or lower-level CMU_Calibrate() function.

According to EFM32G210 datasheet section 3.9.3, the LFRCO accuracy is +/-4.5% and tuning steps are 1.5% typical. That is, you may be off by approximately 1 h / day.

The sync period with downlink messages depends on your required accuracy.
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