LPC11C12 External Clock on XTALIN

[jeremyleaf]

I want to use an external clock source (a 12MHz TCXO) fed into the XTALIN pin of the LPC11C12 microcontroller. This could either be as a clipped sine wave (0.8V peak to peak, no negative swing) directly from the TCXO, or I could put it through a schmitt trigger to get a digital input at whatever voltage level. I read in the datasheet that to do this I should put the XTALIN pin into bypass mode (pg 29 of user manual) to allow this, but there is no mention of required voltage level/duty cycle/digital or sine input etc.

The user manual only says (at multiple points) with relation to the XTALIN pin  - "Input to the oscillator circuit and internal clock generator circuits. Input voltage must not exceed 1.8 V.", but nothing else.

Could anyone help me with this?

Thanks

[jeremyzhou · Accepted solution]

Hi Jeremy Leaf ,

Thank you for your interest in NXP Semiconductor products and 

for the opportunity to serve you.

Please checking the 11.2 XTAL input section in the attachment, I think it's very helpful.

LPC11Cxx datasheet:

https://www.nxp.com/docs/en/data-sheet/LPC11CX2_CX4.pdf

Have a great day,
TIC

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