STM32F411 USB VCP clock settings problem?

[ASchu.4]

Hi,

I'm developing a sensor tag wich uses STM32F411CC and I use an USB connector to communicate with the PC over VCP. I'm using the newest cube, keil, DFP, etc.

After setting the 48MHz clock(for USB) i can't adjust the core frequency - only just to 32MHz, I use an 16MHz crystal for HSE. If I set the clocks(48MHz is untouched) to another value, like 16,48,96 MHz etc, the windows tool manager cant see the device or can't start the device with error code 10. This is still standing when i want to use mass storage usb device. If the clock is not 32Mhz I can't see the device.

I missed something ?

Thanks

Attila

[waclawek.jan]

Read out and check the RCC registers' content, mainly RCC_PLLCFGR. As the 'F4 derive both higher-frequency system clock and the 48MHz clock from two taps of the same PLL, the VCO must be set to a common multiple of these two frequencies and then the P and Q dividers set respectively.

JW