Kinetis ENET PHY erratic MDIO read

[KGooding]

We are using a TWR-K53N512 eval board. We are transmitting and receiving ethernet packets as expected, though communications with the PHY is erratic. Looking on a scope the 2MHz MDC clock is clean, as is the data outputted on MDIO from the K53. Though when a PHY read command is issued the data returned from the PHY is not clean. It rises slowly and then falls immediatelly. Lining up the positive clock edge with the data it has risen to just over half. This results in the K53 randomly detecting data bits. It seems as if something is trying to pull the line low. This occurs on all of our 3 towers.

Any help or ideas welcome.

Regards,

Konrad

[mjbcswitzerland]

Hi

This is a problem with the backplane having too high capacitance, and the pull-up resistor used on the MDIO line being too weak. See also the section "PHY and RMII" in http://www.utasker.com/docs/KINETIS/uTaskerV1.4_Kinetis_demo.pdf

If you program the MIIM clock to run at 800kHz instead of 2MHz it should be fine. The problem is the same for all tower kits using Ethernet.

Regards

Mark

[KGooding]

Mark,

Thank you for the information regarding the ENET PHY MDIO signal. I have reduced the clock to 800KHz and it improves the reliability of PHY reads, though it is not 100% reliable. I have also reduced the clock further and this makes no difference.

Thanks again,

Konrad.

[PaoloRenzo]

Hi

What are your settings for MII communication? Any change at the hardware or using regular TWR boards?

What software are you using? Have you tried with MQX?