KV58 RMII_REF_CLK source

[rowangifford]

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

[xiangjun_rong · Accepted solution]

Hi, Rowan,

I have seen the maximum value 48MHz for Input clock frequency (external clock mode) exactly on data sheet of KV58, I do not know the background of the spec.

But we connect 50mhz clock signal to Extal pin for KV58, no problem.

This is the input clock circuit on TWR-KV58:

Hope it can help you

BR

XiangJun Rong

[rowangifford]

Thanks, we tried with the same clock config as the TWR-KV58 and it seems to work.

The mcuexpresso clock configuration tool may need updating, as it uses the datasheet max EXTAL frequency of 48MHz, so won't let you specify 50MHz external clock.