How to set a NUCLEO G491RE into DFU(Device Firmware Update) mode?

[Jahidur1414]

Hi STM Community,

I’m currently working with the NUCLEO-G491RE board and need some guidance regarding DFU (Device Firmware Update) mode.

According to the documentation, CN2 is marked as the DFU connector. Based on that, I have soldered 4 pins on CN2. I also have a USB Type-C female breakout board, and I’d like to connect it properly to CN2.

USB Type-C Female Breakout Board.

However, I’m a bit confused about the following points:

1. CN2 pin mapping

   • Which pin on CN2 corresponds to GND, D+, D-, and 3.3V / VBUS?

2. Entering DFU mode

   • What are the exact steps to put the NUCLEO-G491RE into DFU (Device Firmware Update) mode?

   • Do I need to configure BOOT0, jumpers, or any CubeMX settings for this?

At the moment, when I connect the board to my PC using the USB breakout, the device is detected as an “Unknown USB Device”, so I assume I’m missing something in either the wiring or configuration.

I would really appreciate it if someone could:

• Clarify the CN2 pinout, and

• Explain the correct procedure to enable DFU mode on the NUCLEO-G491RE.

Thanks a lot in advance for your help and support!
Looking forward to your guidance.

[FBL]

Hi @Jahidur1414 

First, you need to check your hardware setup.

Check if the USB Type-C Female Breakout board has protection circuit, if not you need to provide one. We recommend using instead X-NUCLEO-SNK1M1

[Mike_ST · Accepted solution]

Hello,

CN2 is marqued as "reserved" on the MB1367 board, and is only connected to the ST-Link STM32F7 chip.

So please don't use CN2.

This MB1367 doesn't have a "user" USB port connected to the main chip (STM32G491 on that board), as we have on some others Nucleo 64.

If you're trying to use the DFU mode of the Bootloader, you can try on to access PA11/PA12 on the CN10 connector.

Please check the AN2606 / STM32G491 section.

[Jahidur1414]

Hi again @Mike_ST @FBL ,

Thanks for the clarifications so far — that helped me understand the board limitations much better.

I’ve now prepared a small USB interface board that supports both USB-C and Micro-USB, and it cleanly exposes the following signals:

• 5V (VBUS)

• 3.3V

• GND

• D−

• D+

(see attached image)

My goal now is to connect this interface correctly to the NUCLEO-G491RE in order to use the ROM DFU bootloader of the STM32G491.

I would appreciate guidance on the following next steps:

1. Signal connection to the NUCLEO-G491RE

From what I understand so far, CN2 should not be used, and the USB pins of the STM32G491 are available on CN10.

Could you please confirm:

• Which exact CN10 pins I should I connect to:

  • D+ → PA12

  • D− → PA11

  • GND → ?

  • VBUS (5V) or VBUS sense (if required) → ?

A small pin-to-pin confirmation would be very helpful.

 

2. Powering and VBUS detection

• Should the STM32G491 be powered from:

  • ST-LINK USB (as usual), or

  • The 5V (VBUS) coming from my USB interface board?

• Does the STM32G491 require VBUS to be present on a specific pin for the DFU bootloader to enumerate correctly?

 

3. Entering DFU mode

To activate DFU (system memory bootloader), is the following sequence correct?

1. Set BOOT0 = HIGH

2. Power-cycle or reset the board

3. Connect USB (D+/D−) to PA12 / PA11

4. Device should enumerate as STM32 DFU on the PC

Please let me know if:

• Any additional jumpers are required

• Any pins must be pulled up/down

• Any common pitfalls exist when using an external USB connector like this

 

4. USB-C considerations

My USB-C breakout includes CC resistors and basic protection, but if there are minimum requirements (pull-downs, ESD, etc.) specifically needed for DFU reliability, I’d appreciate your advice.

---

Thanks again for your support and patience.
just want to be sure I’m connecting and booting the device correctly.

[Mike_ST]

Hi again,

I have never tried such a setup,

but from what I read, I don't see immediatly anything wrong.

• GND → any ground pin.

• VBUS sense (if required) →  VBUS sense not needed

• VBUS (5V) → depends of how you power the board → maybe try not to connect it if the board is powered from the ST-Link connector.

Just for the "3. Entering DFU mode", the STM32G4 has some option bytes to select the boot mode. Either the boot selection (main flash or boot rom) is taken from the Boot0 pin, either it taken from the option bytes settings.

As far as I know on the MB1367, the option byte approach is chosen when the boards are manufactured, so setting JP7 might not help.