External oscillator before FXOSC configuration

[via]

I am trying to use an external quartz oscillator with an S32K344, instead of using a standalone quartz crystal.  The reference manual notes, "When the FXOSC is used in Bypass mode, the external clock source can only be enabled after the FXOSC is enabled."  

Does this mean that, with a 4-pin oscillator where one of the pins is an enable pin, I need to use a GPIO to not enable the oscillator until FXOSC is enabled (OSCON is set) and in bypass mode? I would instead prefer to hardwire the oscillator to always be enabled, what will happen if a clock is provided to EXTAL before FXOSC is enabled and put into bypass mode?

[Robin_Shen · Accepted solution]

Hi

Sorry. Since S32K3XXRM has clearly mentioned the following requirements, I'm afraid you can only follow the instructions:

28.1.1 Chip-specific FXOSC information
For bypass mode applications, the EXTAL pin should be driven low when FXOSC is in off/disabled state.
•While initializing FXOSC: When the FXOSC is used in Bypass mode, the external clock source can only be enabled after the FXOSC is enabled.
•While disabling FXOSC: When the FXOSC is used in Bypass mode, the external clock source must already be inactive before disabling the FXOSC.

Best Regards,
Robin
-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------