ESP32 Forum

Hi!
Please help me to figure out the ethernet interface implementation of LAN8720 PHY in the ESP-IDF. Specifically my question is about the RXER pin of LAN8720.
I have the WT32-ETH01 board. And the ESP32-S1 module's IO13 pin is attached to the RXER pin on LAN8720 with a 10K pull-up resistor.
At the same time Waveshare's LAN8720 module have just pulled-up this RXER pin and it is not exposed to the connector.

I was not able to find the usage of the RXER pin in ESP-IDF ethernet implementation. Did I miss its usage somewhere?

The reason this RXER pin got my attention is the JTAG interface. At the WT32-ETH01 board the IO13 pin is occupied by RXER signal and it blocks JTAG debugging (which I miss a lot ). JTAG pins can not be remapped. So I wonder if I cut the IO13 pin of ESP32 module from PHY chip and will use it for JTAG, will the the ethernet functionality remain working correctly.
Also this knowledge will be useful for custom board designs. It seems that RMII interface does not require RXER pin, but if so why LAN8720 exposes it and WT32-ETH01 has connected RXER to ESP32?

RXER signal is not used by current ESP-IDF Ethernet drivers.

Hi morphal, thanks for the interesting post, were you successfull in cutting the IO13 pin of ESP32 module from PHY chip and using it for JTAG?
Thanks!

momentous wrote: ↑

Mon Mar 11, 2024 2:19 pm

Hi morphal, thanks for the interesting post, were you successfull in cutting the IO13 pin of ESP32 module from PHY chip and using it for JTAG?
Thanks!

Hi! Sorry for late reply but better late than never)
Yes, this connection is not used by LAN8720. You can cut it and use IO13 for JTAG. It worked for me

Great, thank you very much! This is excellent