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STM32F105 in USB Device Mode not recognized by PC

Question asked by moardy on Nov 30, 2012
Latest reply on Nov 30, 2012 by moardy

I am trying to connect an F105 via USB on a PC. But the F105 is only recognized when I put an external 1,5K pullup resistor on the USB D+ dataline.
Unfortunately, the same MCU is also used as an USB host for storing data on an USB pen drive. But when I tried this, the pen drive is only recognized, when the 1,5K resistor is

My question: how do I activate / deactivate the internal pullup resistors of the F105?

Trying to switch the Pull-Up resistor with a GPIO pin is not an option - the hardware design
has finished.

Thanks for every help!