32K crystal can't generator RTC clock

[lifeng]

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.

[kerryzhou]

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

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[lifeng]

 Hello Kerry Zhou:

      After change 32k SPXO, the RTC work normal.

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

[kerryzhou]

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

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[lifeng]

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

Why the 32K crystal can't work?