F767: USB Device DFU crystal 8 MHz

[HMSEdinburge]

Hello.. Anyone can advise if using USB Device for DFU, which crystal should i use? 25MHz? Why i dun see the 25 MHz crystal on 767 Nucleo ? 

if i only include the 8 MHz crystal (as the main clock )is it fine to drive the USB Device DFU? Please advise? 

[STOne-32]

Dear @HMSEdinburge ,

Yes, you can use 8MHz crystal for the HSE ( main Oscillator) for STM32767 MCU and having USB Function.  it is even better if using internal Bootloader.

25MHz is used for Ethernet Usage to have either MII or RMII clock on board, if not the case.  8MHz is enough for USB and all system clocks.  In fact, the PLL and pre-scalers will do the right settings to have the selected frequency up to 216MHz .

See Table 94 : Introduction to system memory boot mode on STM32 MCUs - Application note for Internal bootloader requirements and the Note at the end.

Hope it is helping you.

STOne-32.