ESP8266 Community Forum

- Fri Sep 07, 2018 4:31 am #78131

I just do not know why GPIO15 (D8) can not be used for this module. For SPI display it works fine. Actually it also stuck programming when it's connected to module.

most likely the CS pin has different behaviour during reset / until init on ethernet than on lcd.
Maybe too strong pullup, gpio15 has to be low during reset.

- Sat Sep 08, 2018 5:54 pm #78147

I just do not know why GPIO15 (D8) can not be used for this module. For SPI display it works fine.

Petrkr,

Just as Shufti says, the W5500 has a pull-up resistor which, if the CS is connected directly to GPIO15, will force the ESP8266 into SDIO mode, which means that it won't do a normal boot from flash.

You -can- use GPIO15, even with boards like the W5500 which have a pull-up resistor; you just need to buffer the output of the pin so that the pull-up isn't "seen" by the ESP8266 (effectively, you are ensuring that the pin can only ever be an output and never an input).

Please look at the link (already posted above) for the (very simple) one transistor circuit to make this work:-

https://esp8266hints.wordpress.com/2018/02/13/adding-an-ethernet-port-to-your-esp-revisited/

- Sat Sep 08, 2018 8:37 pm #78148 No buffer needed. Just remove the pull up resistor.