K64F Must use external 50MHz Ethernet clock?

[joelk]

Is the K64F MCU capable of generating the 50MHz clock for RMII Ethernet?

I'm trying to avoid adding a crystal to generate this clock in the PHY.

[mjbcswitzerland · Accepted solution]

Joel

You "need" to have a 50MHz clock signal on CLKIN, which is internally connected to the MII clock line, in order to use Ethernet in RMII mode.

There is however no need to have two crystals/clocks due to this - just choose a PHY that accepts a 25MHz crystal and supplies the 50MHz clock to the K64 input (eg. KSZ8081RNA).

You just need to allow the PHY to come out of reset so that it can start up and supply the Kinetis clock,

I have worked on several K60, K64, K61, K70 products using this strategy and there are no problems - and the only crystal required is the one at the PHY.

If you have to avoid generating the clock at the PHY you can also use an external 50MHz oscillator - with a PHY requiring the clock as input (as is done on the K60 tower kit). It is important that the same oscillator source is used for both (synchronised).

Regards

Mark

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