I have a PCB prototype which uses an ESP8266 module, ESP-01, the first ESP model with a 4x2 male pin header, and I will interface the ESP with a microcontroller.
My main doubt is about GPIO0 pin of this module. GPIO0 is floating on my PCB. I measured the voltage on it and observed 3.3V. Ok, it should have an internal pull-up resistor on the module. But the question is: can I, WITH SURE, leave GPIO0 floating? (considering that I don't want to flash the ESP memory via UART). Does all ESP modules have internal pull-ups at these 2 pins?
The other GPIO of ESP-01, 'GPIO2', is connected to an I/O of the MCU and that I/O of the MCU is configured as output and driving logic 1 (3.3V) to the GPIO2 pin. Maybe it would be better to configure this I/O of the MCU as digital input... Do you have any observation about putting that I/O of the MCU as output?