Wrong boot mode detected (0x1b)! The chip needs to be in download mode.

[markj]

I have seven ESP32 PoE ISO boards here, all of which are unprogrammable because they all give the error: A fatal error occurred: Failed to connect to ESP32: Wrong boot mode detected (0x1b)! The chip needs to be in download mode.

How can I resolve this issue?

Many thanks
Mark

[LubOlimex]

7 out of how many?

It can be software related (either programming software, or drivers, or operating system). Try programming the boards with another software and another USB cable and maybe another computer. If the issue remains:

- Maybe some attached peripheral holds the bootstrap pins responsible for the boot mode in wrong state. Try disconnecting any extra peripherals attached to the board.

- By default the board automatically enters bootloader mode on power up and reset, however this can also be forced but requires altering the wire so that user button BUT1 acts as bootloader button. You need to remove resistor R48 and solder R49 pads together. This way BUT1 would be connected to D_COM and act as boot button. Refer to the schematic and check the part "Buttons" to understand better. Once you've removed R48 and soldered R49 together - you can force bootloader mode by holding button BUT1 pressing reset and releasing reset. Force bootloader that way before trying to upload your software.

[markj]

So I have 13 ESP32 boards in total, and 7 exhibit this problem, and 6 I can program without issue.I'm using the same software and cable for all.

[LubOlimex]

Making the user button a boot button would probably help with this issue. Maybe try on one of the boards what I explained above - unsolder R48 and solder it on R49 pads, then force bootloader mode via the button (hold the button pressed, press and release reset, release the button).

If you are not keen to solder, maybe first try with another computer. Very common issue is incompatibility between the driver and the operating system and the tool used for programming (which is usually esptool). This causes timing and timeout issues during upload, if the values are too close to the timeout sometimes it might work, sometimes it might fail, some boards might work, some might not. Trying with latest version of esptool and drivers and another OS would also probably fix the issue. Maybe also try another USB cable and different USB ports,

It is a popular problem make sure to also search online for "A fatal error occurred: Failed to connect to ESP32: Wrong boot mode detected (0x1b)!".