How do I use CUBEMX to develop STM32F400?

maybe - because F400 is not existing cpu (by STM) . maybe is a board by Keil .

try STM32F407 to select cpu.

Learn Chinese, read the docs, either get Chinese CubeMX with F400 support or alternatively work with normal CubeMX F410 project. Check for differences between the two chips in the respective datasheets if any such differences exist. ;)

>>I can not find it.

Link to a board or MCU reference to whatever it is you're talking about.

Seems like a Chinese market device lacking QSPI, CRYP, USB, CAN and ETHERNET IP and limited memory.

Might be a subset of the F41x, I'd imagine there are HAL, or libraries available to the primary customers of this device.

Perhaps probe it a little?

Query the DEV_ID ? Look at the ROM code ?

Cross reference data sheet information with others, and reference manuals

https://datasheet.lcsc.com/lcsc/2204211700_STMicroelectronics-STM32F400RBT6_C2965704.pdf

Hello PP.7,

Thank you for contacting STMicroelectronics. Regarding your inquiry, please see product page for the STM32CubeMX below:

https://www.st.com/en/development-tools/stm32cubemx.html

There you will find the documentation tab which contains the documentation such as user manuals to assist your development.

Should others on the forum have similar inquiries, please feel free to submit a customer support ticket on the ST support page for further assistance.

Kind Regards,

ST Support