topic Re: K60 OSC032CLK / reference timing in Kinetis Microcontrollers

K60 OSC032CLK / reference timing

tiborsomogyi — Thu, 10 Nov 2016 18:17:09 GMT

Hello,

I am working with the TWR-K60F120M board ( MCU=MK60FN1M0VLQ12 ) as "proto board" for my project, and would like to avoid the 32 kHz RTC oscillator for my final design. However, the final design requires a quite precise time-keeping function, so I wonder whether I can make it from other sources. One of the promising signals is OSC032KCLK - an output signal from System Oscillator 0. With such a name I could expect that it is a 32.768 kHz clock with quartz precision - but the Reference Manual does not say too much about this clock. So my question(s) are:

- Is this OSC032KCLK clock is an 32.768 kHz signal independently of the external crystal / oscillator feeding System Oscillator 0 ? ( e.g. what will be the frequency of OSC032KCLK if I feed System Oscillator 0 with the 50 MHz external oscillator on the board ? )

- If the response to the previous question is that OSC032KCLK has the same frequency than the input signal, my understanding is that I could use other time references, such as LPO or MCGIRCLK - this later is even trimmable. Does someone have some experiences of using these time references ? I would like to know whether I can count on their stability ( these are not based on some quartz resonators ), mainly under varying temperatures ( 40 ..120 degC )

Thanks and regards

Tibor

Re: K60 OSC032CLK / reference timing

mjbcswitzerland — Thu, 10 Nov 2016 20:22:32 GMT

OSC032KCLK is available only when a 32kHz range crystal is used as crystal for OSC0. This can be used in some low power modes. Ref: https://community.nxp.com/message/398196#398196

If you require battery backed up RTC you need to use the RTC oscillator.

In case you don't need low power or power down RTC you can use a 1Hz interrupt from any timer for RTC function.

LPO etc. have large drift (resolution and temperature dependency) for long term time keeping and so are not advised

Regards

Mark
Kinetis for professionals: http://www.utasker.com/kinetis.html
http://www.utasker.com/kinetis/TWR-K60N512.html
http://www.utasker.com/kinetis/TWR-K60D100M.html
http://www.utasker.com/kinetis/TWR-K60F120M.html
http://www.utasker.com/kinetis/ELZET80_NET-KBED.html
http://www.utasker.com/kinetis/ELZET80_NET-K60.html
Time keeping: http://www.utasker.com/docs/uTasker/uTasker_Time.pdf

Re: K60 OSC032CLK / reference timing

tiborsomogyi — Mon, 14 Nov 2016 10:50:38 GMT

Thank you Mark. I think that as you suggest, I'll use a timer IT...

Cheers

Tibor