Reserved GPIO’S

Some GPIO’s cannot be used freely, as they are already assigned to module peripherals or have special functions during booting:

GPIO0 pin is used as a bootstrapping pin, and should be low to enter UART download mode. Make sure it is not pulled low by a peripheral device during boot or the firmware will not start!

GPIO2 pin is used as a bootstrapping pin, and should be low to enter UART download mode. Make sure it is not pulled high by a peripheral device during boot or you will not be able to flash a firmware to the module!

GPIO06 through GPIO11 are reserved for the FLASH. You cannot use them at all!

GPIO12 is used as a bootstrapping pin to select output voltage of an internal regulator which powers the flash chip (VDD_SDIO). This pin has an internal pulldown so if left unconnected it will read low at reset (selecting default 3.3V operation). Make sure it is not pulled high by a peripheral device during boot or the module might not be able to start!

GPIO34-39 can only be set as input mode and do not have software pullup or pulldown functions

GPIO37 and 38 are not available on most modules

ESP32-PICO-D4:

GPIO16 and 17 are used for internal Flash (Readers input)

ESP32 WROVER:

GPIO16 and 17 are used for the PSRAM

 

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3 comments

  • pit

    On ESP32-PICO-D4:
    Don’t use GPIO16 and 17, because they used for the internal Flash.

    PS: great wiki, thx

    Reply
  • alien

    What to do with unused pins on esp boards? Normally unused pins should be set as INPUT_PULLUP.
    So pins GPIO34-39 need external pull up?
    What with GPIO06 through GPIO11 ? When I set them this way esp cannot start(stil reset).
    But what do with pins 0, 2, 5, 12 ? They have pull up/down probably after start?

    Reply
    • beegee1962

      You should ask that question directly to Espressif, I cannot answer what the state of the GPIO’s is after power-up/reboot.
      Just from experience, I don’t assign unused GPIO’s to anything and my ESP32’s are just running fine.

      Reply

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