STM32F207 ethernet issue using with ksz8091 transceiver

[sunilhalvi]

Hi STM community,

We are using the microchip KSZ8091RNA Ethernet transceiver chip with the STM32F207 controller. We have a working firmware that we tested with LAN8740A transceiver chip. Now, in our new design we have used KSZ8091RNA. The issue is
1) Link status is always down in register 0x01.
2) The pins TXP, TXN, RXP and RXN are not generating expected signals. TXP and TXN are generating the same signals, RXP and RXN are generating same signals. However, TX and RX pins generate differential signals.

We are using STM32CubeIDE 1.18.1 and Code configurator STM32CubeMx v6.14.1

We have attached oscilloscope screen shots for reference. We have attached driver schematics and layout for your reference. Kindly, help us to resolve this issue.

[STackPointer64]

Hello @sunilhalvi, and welcome to ST Community!

I noticed your crystal oscillator specs differ a bit from the recommended ones, your chosen oscillator has the same frequency (25 MHz) and actually a better frequency tolerance (10 ppm vs 50 ppm), which is great for stability.

However, there are two points to watch out for:

• Series Resistance:
  Your oscillator’s series resistance is 50 Ω, slightly higher than the recommended 40 Ω. This could make the oscillator a bit harder to start or sustain oscillation, potentially causing longer startup times or unstable clock signals.

• Load Capacitance:
  The load capacitance you have is 10 pF, but the recommendation is 16 pF. Using a lower load capacitance usually shifts the frequency higher than expected, which might cause timing issues or communication errors in your system.

The PHY is very strict when it comes to timing. That is why you should try to adjust the external load capacitors on your board to get closer to the 16 pF load capacitance.

Best regards,