Getting the into Download Mode is a fundamental step for flashing firmware , yet it remains one of the most common hurdles for developers. Whether you're dealing with a board that won't auto-reset or building custom hardware, understanding the "strapping pins" and manual sequences is essential for a smooth workflow. Core Mechanism: The Bootloader and Strapping Pins
If your development board fails to enter Download Mode automatically when you click "Upload" in your IDE, use one of these manual sequences:
Other pins that must be in a specific state at boot include: Must be LOW or floating. GPIO5: Must be HIGH. GPIO12 (MTDI): Must be LOW. GPIO15 (MTDO): Must be HIGH. How to Enter Download Mode Manually
Boot Mode Selection - ESP32 - — esptool latest documentation
The ESP32's behavior at startup is determined by the state of specific . The ROM bootloader samples these pins during power-on or reset to decide if it should boot from internal flash (standard operation) or enter Download Mode (UART flashing). The primary pin governing this is GPIO0 . Download Mode: GPIO0 must be LOW (grounded) during reset.
GPIO0 must be HIGH (3.3V) or floating.
