ESP32 Forum

I'm exploring adding Ethernet to my ESP32 board and came across this reference:

https://techoverflow.net/2021/07/25/esp ... reference/

It claims GPIO16 and 17 are part of the interface pins. But IIRC, these two pins are used as CS pins for PSRAM. Does this mean I can't use PSRAM if I use Ethernet? Just curious. Thanks.

I've seen other ESP32 pins marked as EMAC pins but this reference doesn't mention them, including pin1 that is used for programming. Does it mean this list is the minimal required pins?

GPIO 16/17 can be configured as output to RMII REFCLK. However, these pins can be also programmed for different usage like PSRAM. Therefore be very careful when you are making a decision which ESP32 module to use.

For example, if you wanted to use ESP32 module with Ethernet and you needed to use ESP32 internal RMII REFCLK (i.e. to use GPIO16 or 17), choose ESP32-WROOM. If you wanted to use ESP32 module with Ethernet, you needed PSRAM and you had an option to use external RMII REFCLK (either generated by external oscillator or provided by PHY), you can use ESP32-WROVER module with PSRAM. Note that external RMII REFCKL inputs to ESP32 via GPIO0, which has also its limitations which needs to be taken into account when you designing the board. However, that's different story...

To make it even more complicated, you could also use GPIO0 as output of internal REFCLK instead of GPIO16/17. However note, it is just experimental feature. Please see https://docs.espressif.com/projects/esp ... -selection and https://docs.espressif.com/projects/esp ... ac-and-phy for more information.