On the Pinout Cards, Some IO Are Listed as Strapping Pins. What Does That Mean?

A strapping pin is a pin/IO that is used by the ESP32 during its boot up cycle to set certain modes.

For example, IO0 is a strapping pin that is read during boot to determine if the ESP32 should enter download mode, or boot and run user code.

You are not allowed to alter it with a pullup/pulldown during boot, or it will not allow you to boot properly. You can only use these pins after your code is running.

For more detailed information about strapping pins, please refer to the official datasheets from Espressif for the ESP32, ESP32-S2, and ESP32-S3.

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Updated on: July 31, 2023

strappin bootstrap bootpin io0