STM32 and KSZ846x ethernet switch chip no link indication

[Peter_TEC]

Hello everybody!

Is anybody tried to connect an STM32 to an KSZ846x (for ex. KSZ8463 - 3 ports ethernet chip MAC+PHY) chip?

I have a very strange issue. I am able to communicate with the KSZ chip using MIIM and also over SPI, and I am able to start the ethernet link auto-negotion, even the chip MAC indicates that the Link is UP, with 100Mbit / Full Duplex. BUT! The Link Activity LED on the KSZ switch chip does not turn on and it is not able to send/receive any packages (over the LAN cable).

I did check the LED indication configuration in the KSZ chip, it should turn on the Link LED when the link is UP by default.

Can it be a hardware error? Maybe the isolation transformer is not working?

My design uses a Bel Fuse S558-5999-U7 isolation transformer... Any suggestion how to debug?

[Piranha]

Check thoroughly if the twisted pairs are routed properly (not swapped TX/RX and not inverted +/-) on PCB and cable. Also check the soldering and cable reliability.

[Peter_TEC]

Hello!

Thank you, that was already checked :) Even swapped pairs should anyhow work, since the chip supports Auto MDI MDIX protocol - able to swap RX/TX by hardware.