Where is the external reference clock reference in the FRDM-K64F?

[arturoluis]

I'm looking at the clocking diagram for the K64F and I don't know which signal is the external reference clock

When the reference manual refers to "external reference clock" in other chapters, is it refering to OSCERCLK or ERCLK32K or other signal??

[mjbcswitzerland]

Hi

"external reference clock" is 'generally' OSCERCLK
ERCLK32K is sometimes known as the "secondary external reference clock"

However, for the MCG, "external reference clock" can be OSCLK (effectively OSCERCLK, which is an optionally  gated version of it), the RTC oscillator or IRC48MCLK - it depends on which one it switches to its input.

Therefore when it is related to the MCG you will need to know which source your are selecting to know what is meant by "external reference clock" - this would be the most correct use of the term. In general cases that are not related to the MCG you can assume that OSCERCLK is very probably meant (it also needs to be switched though for it to be actually be available though).

Only rarely would it mean ERCLK32K - but probably only when taken out of context.

In each case you should find that the specific names like OSCERCLK, LPO, ERCLK32K are used precisely somewhere that confirms exactly the source being used.

Regards

Mark