A basic question on clock

[ryang]

In some documents, I read that

The module is designed to operate at 12 MHz using the free running (non
phase selected) clock.

What does the term free running clock mean? I am not very clear.

Does anybody give me some hint?

Thank you in advance

 

[farhada]

Hi,
Free running means it is not locked into another source and it is not synchronized by any means.

Any crystal oscilator is a free running clock, but an oscilator with an outside source via PLL, is not.

The problem with free running clocks is that if you have 2 sources with the same frequency runing at 2 different oscilators, after a while, these 2 will get away from each other and are not synchronized. This can cause a lor of problems if you are dealing with datasharing and communication between the 2 in high speed.

Hope this helps a bit,

Best regards,
/Farhad