Kinetis Microcontrollers中的主题 32K crystal can't generator RTC clock

32K crystal can't generator RTC clock

lifeng — Thu, 20 Jul 2017 01:57:36 GMT

MKE18F512VLL16， the 32k crystal can't generator rtc clock.

add a 1M resistance between PTC3 and PTC2, the PTC3 wave is

The PTC2 have no wave.

I had a TWR_KE18F board，it not install the cap and resistance ,and the wave is well, why?

If get rid of the cap and resistance in my board ,the wave frequency is 1.4M, and the amplitude is very low.

The same code download to the TWR_KE18F , the RTC wave is well, so the problem is not the code.

Re: 32K crystal can't generator RTC clock

lifeng — Sun, 23 Jul 2017 03:36:31 GMT

Now use LPO clock (128k/128=1k) for RTC, the RTC can work normal。

Why the 32K crystal can't work?

Re: 32K crystal can't generator RTC clock

kerryzhou — Tue, 08 Aug 2017 02:01:31 GMT

Hello Li feng,

From your description, your problem is caused by your external RTC hardware or circuit.

1. About the layout, you can refer to this document:

http://cache.nxp.com/docs/en/user-guide/KLQRUG.pdf?fsrch=1&sr=1&pageNum=1

Chapter 2.1.3.3 Oscillators.

2. About the load capacitor

Please check your 32.768K crystal datasheet, find the proper load capacitor.

Both PTC2 and PTC3 should have the 32K oscillating wave.

TWR-KE18F board didn't add the external capacitor, it should be the board layout parasitic capacitance is enough for the oscillating.

Wish it helps you!

Have a great day,
Kerry

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Re: 32K crystal can't generator RTC clock

lifeng — Wed, 01 Nov 2017 02:59:38 GMT

Hello Kerry Zhou:

After change 32k SPXO, the RTC work normal.

So the 8M and 32k crystal all change SPXO.

Re: 32K crystal can't generator RTC clock

kerryzhou — Wed, 01 Nov 2017 06:33:03 GMT

Hi Li Feng,

Thank you for your updated information.

So, it seems still the crystal hardware match problem on your side.

Have a great day,
Kerry