K20 RTC CRYSTAL PINS XTAL32 & EXTAL32 has no voltage

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K20 RTC CRYSTAL PINS XTAL32 & EXTAL32 has no voltage

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markkalior
Contributor II

I see no voltage on the K20 RTC pins XTAL32 & EXTAL32.  The BSP does turn on this External Crystal. 

Any have any idea why?

I am expecting about 1/2 voltage.

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793 次查看
danielchen
NXP TechSupport
NXP TechSupport

Hi Kalior:

I think  first you need to check the register OSC_CR ,   Bit 7 ERCLKEN , make sure that external reference clock is enabled

Then you can check the MCG control 2 Register, what is the value?

Regards

Daniel

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markkalior
Contributor II

If the System Osc isn't being used, still set the OSC_CR, bit 7?  I have tried both ways.   Currently, I have it set to zero.   MCG_C2 = 0, MCG_C7=0x01.   Which should select the XTAL32 & EXTAL32, instead of the XTAL0 & EXTAL0. 

Will the RTC work at all, if the VBAT is flowing?

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danielchen
NXP TechSupport
NXP TechSupport

You are right. If the system OSC isn't being used, you do not need to set the OSC_CR , bit 7.

RTC is powered by VBAT.

MCG_C2 = 0 and MCG_C7 =0x01, that is OK

Please also check the RTC Control Register (RTC_CR)

You need to enable OSCE:  Oscillator Enable;    configure the CLKO, according to your requirement.

SC20, SC4P, SC8P, SC16P, you need to configure them according to the schematic.

Regards

Daniel

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markkalior
Contributor II

I do have RTC_CR, bit OSCE set to a one. 

Do you know if the any of the RTC registers will work, if VBAT is flowing?

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danielchen
NXP TechSupport
NXP TechSupport

Yes, if VBAT is flowing, the RTC registers can be accessed. But when the chip main power lost, the core doesn't work and couldn't access the RTC registers.

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