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KV58 RMII_REF_CLK source

Question asked by Rowan Gifford on Mar 13, 2018
Latest reply on Mar 14, 2018 by Rowan Gifford

Hi,

 

The RMII interfaces requires 50Mhz clock source, we use a PHY which provides this.

 

The reference manual says the RMII clock source can be EXTAL clock or ENET_1588_CLKIN selected via SIM_SOPT2[RMIISRC]  (page 172), so we have routed the PHY clock source to the EXTAL pin and configured SIM_SOPT2 to use EXTAL as a source.

 

However datasheet section 3.3.2.2 Oscillator frequency specifications states fec_extal Input clock frequency (external clock mode) to be 48Mhz max.

 

So can a 50Mhz clock source be fed into EXTAL input, or is ENET_1588_CLKIN the only valid RMII clock source?

 

Many thanks,

Rowan

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