I've just assembled a PCB with a ESP32-S3 on it. It has the buttons for reset and boot, but when connected by UART it gives the following output in a loop when reading serial.

invalid header: 0xffffffff
Build:Mar 27 2021
rst:0x10 (RTCWDT_RTC_RST),boot:0x9 (SPI_FAST_FLASH_BOOT)
invalid header: 0xffffffff
invalid header: 0xffffffff

It does not let me upload code, neither by using Espressif IDE nor Arduino IDE (even when pressing the reset or boot button).

My guess is that maybe the chip got damaged when using the hotplate while soldering the chip to the PCB. I connected the "boot" button into the GPIO0 pin with a pullup configuration, as well as the EN pin (reset).

  • 1
    \$\begingroup\$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. \$\endgroup\$
    – Community Bot
    Aug 23, 2023 at 18:32
  • 1
    \$\begingroup\$ Provide schematics what is connected to each and every MCU module pin. \$\endgroup\$
    – Justme
    Aug 23, 2023 at 18:51
  • \$\begingroup\$ With what command and tools are you trying to upload code? \$\endgroup\$
    – Codo
    Aug 23, 2023 at 19:36
  • \$\begingroup\$ This 0xFFFFFFFF could be a hint, that the RX input is permanent low. \$\endgroup\$
    – Jens
    Aug 23, 2023 at 22:26

1 Answer 1


I found the issue, basically for the ESP32 to be able to enter boot mode, the IO46 must be pulled down, as well as the SPI boot (the "boot button" connected to IO0), otherwise it would "trigger unexpected behavior". I just didn't include that routing when designing the PCB.

I will add a picture from the documentation and a schematic I found on internet.

Chip Boot Mode Control

ESP32 reset and boot connection

  • \$\begingroup\$ "I will add a picture from the documentation and a schematic I found on internet." If you use external sources, you must disclose them. \$\endgroup\$
    – Velvet
    Sep 1, 2023 at 6:33

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