How to connect an external clock source

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How to connect an external clock source

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masahirokiniwa
Contributor IV

Hi,

ICould you tell me how to connect external clock sources?

I'll use i.MX RT1064 with external clock sources for 24MHz and 32kHz.

I check the below thread and see the connection to XTALO and RTC_XTALO, but I'm not clear the connection of XTALI and RTC_XTALI.

I confirm its reference manual 14.4.2 and 14.5.2, and I think that I should connect it to capacitor.

Could you tell me the suggested capacitance value and the connection with reference circuit?

https://community.nxp.com/message/1155008#comment-1156814 

best regards,

M.Kiniwa

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jeremyzhou
NXP TechSupport
NXP TechSupport

Hi Masahiro Kiniwa,

Thanks for your reply.

1) Should I connect an external oscillator to RTC_XTALI and RTC_XTALO should be left floating as below #2?

-- Yes.

Have a great day,
TIC

 

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simondelaney
Contributor I

Hello,

I am connecting an external 24 MHz clock to the i.MXRT1064. The datasheet (table 3) states this must be connected to XTALO, with an 18pF capacitor from XTALI to ground.

The reference manual (15.4.2) says there are three options for this connection, but the preferred one is to connect the external clock source to XTALI and leave XTALO floating.

The block diagram in the reference manual indicates either should probably work. I don't see why the options described in the reference manual shouldn't work, but the datasheet does not agree. I do not want to find the microcontrollers on my boards just don't run at all and there's nothing I can do about it.

Can you please clarify which of the above options will/won't work (given a suitable clock source)?

What are the relative merits of the options that will work?

Thanks,
Simon

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masahirokiniwa
Contributor IV

Hi Simon,

I'm using an external oscillator and my board is operating by it.

I'm connecting the external oscillator to XTALO and the XTALI mounted with 18pF capacitor as the datasheet.

Best regards,

M.Kiniwa

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jeremyzhou
NXP TechSupport
NXP TechSupport

Hi Masahiro Kiniwa,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
Please check the guide for the external clock source circuit design.

pastedImage_1.png

Have a great day,
TIC

 

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masahirokiniwa
Contributor IV

Hi jeremyzhou ,

Thank you for your answer.

I see about 24MHz, I'll connect an external oscillator to XTALO and connect 18pF capacitor to XTALI.

About RTC oscillator, should I connect an external oscillator to RTC_XTALI and RTC_XTALO should be left floating as below #2?

pastedImage_2.png

Best regards,

M.Kiniwa

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jeremyzhou
NXP TechSupport
NXP TechSupport

Hi Masahiro Kiniwa,

Thanks for your reply.

1) Should I connect an external oscillator to RTC_XTALI and RTC_XTALO should be left floating as below #2?

-- Yes.

Have a great day,
TIC

 

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Note:
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- We are following threads for 7 weeks after the last post, later replies are ignored
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