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ENET_REF_CLK (ball V22) duty-cycle requirements on i.MX6

Question asked by Grant Fordham on Jun 16, 2015
Latest reply on Jun 16, 2015 by Clemens Gruber

Hi,

 

I would like to know the duty-cycle requirements for the ENET_REF_CLK input in RGMII mode. We are using the KSZ9031RNX PHY which has the following errata:

 

The 125MHz reference clock (CLK125_NDO pin) output

has duty cycle variation when the KSZ9031 links up in

1000Base-T Slave mode, resulting in wide variation on

the falling clock edge.

 

Has anyone successfully used this PHY with the i.MX6 while driving ENET_REF_CLK from CLK125_NDO output of the PHY?

 

One of the workarounds is to only use the rising edge of the clock provided on CLK125_NDO, but I'm unsure how exactly ENET_REF_CLK is used internally. Does it drive RGMII_TXC directly or is there a PLL in between?

 

There is a similar question from Clemens Gruber at the link below, but the question as to how ENET_REF_CLK is used internally and exactly what the duty cycle requirements are has not been answered. BTW, thanks Clemens Gruber for alerting me to the KSZ9031RNX errata

 

i.MX6Q ENET.REF_CLK input

 

Regards,

Grant

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