Entering the Bootloader

Espressif chips have to be reset in a certain way in order to launch the serial bootloader, only then can esptool.py communicate with the ESP chip.

On some development boards (including NodeMCU, WeMOS, HUZZAH Feather, Core Board, ESP32-WROVER-KIT), esptool can automatically trigger a reset into the serial bootloader - in which case you don’t need to read this section.

For everyone else, three things must happen to enter the serial bootloader (firmware download mode) - a reset, required pins set correctly, and a correct strapping pin pulled low. For more information, see the detailed Boot Mode Selection guide.

Boot Mode

Espressif chips choose the boot mode each time they reset. A reset event can happen in one of several ways:

  • Power applied to chip.

  • The CH_PD/EN pin (“enable”) pin was low and is pulled high.