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STM32f070f6 won't show up as serial communication device class

Question asked by andreas kellermann on May 19, 2017
Latest reply on May 22, 2017 by andreas kellermann

I have a board with a STM32f070f6 which won't show up as communication device class on the usb port.

I tried to make it work without activating the usb and the LED blinks just fine (programing via usb/dfu file which indicates to me that the oscillator must be working?).


What I have done:


Connect 8MHz 3.3V CMOS oscilator: 

ASEMB-8.000MHZ-XY-T Abracon LLC | Crystals, Oscillators, Resonators | DigiKey 

with a short trace to the PF0 pin and set the PF0 pin to High Speed Bypass input. PF1 is greyed out which I assume means high-impeadance state(?)


I checked the oscillator and the square wave is stable to about +/-5ppm, has 50% duty cycle, starts up after about 1ms and goes from 0V to 3.3V in it's high state with some ringing which should be well inside the 0.2* and 0.8*VDD specs given for the STM32f0. I do not see anything wrong here (see oscilloscope screenshots and settings files).


The heap and stack size was also increased to 0x400 and 0x800 since this caused some problems before.


I would be glad if somebody would have a suggestion of what to try?