External crystal failure detection in LPC546xx

[prasannanaik]

Hi,

   I am using LPC54608J512BD208 in an application. The controller clock is derived from external crstal of 20 MHz and stepped up through PLL at 100 MHz. Is there any way to detect the external crstal failure so that the controller can be switched to internal clock FROH.

Thanks and best regards,

Prasanna

[jeremyzhou]

Hi Prasanna Naik,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
Do you mean whether there's a mechanism that can switch the clock mode automatically when MCU detects a clock failure signal? If yes, I'm afraid it doesn't exist this mechanism.

Have a great day,
TIC

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[prasannanaik]

Hi Jeremy,

   Thanks for your help.

   I don't want automatic changeover on failure. I want to know how to detect the crystal failure in firmware so that we can switch over the controller to FROH manually.

Thank and best regards,

Prasanna

[brendonslade]

Hi Prasanna,

I havent tried this, but it should work... you can use the frequency measure function to check the xtal as part of your start up. You can use the frequency measure function to check the xtal (using the FRO as a reference) is working as part of a start up diagnostic. Start up your system using the FRO, run the diagnostic, then switch to the xtal if it all looks ok. See section 10.6 of the chip user manual for info on that frequency measurement function.

If you need to detect and recover from a xtal failure while the application is running then you could use a watchdog timer to restart the system if it crashed due to the xtal.

Hope that helps.

regards,

Brendon

[jeremyzhou]

Hi Prasanna Naik,

Thanks for your reply.
Whether you mean that code detects the crystal failure, then switch over the controller to FROH, if yes, it's impossible actually.

Have a great day,
TIC

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