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STM32F107 USB Virtual Com Port - problem

Question asked by otachkin.alexey on Dec 19, 2012
Latest reply on Dec 27, 2012 by otachkin.alexey
I have a problem using USB as Virtual Com port on STM32F107. I use example code for USB CDC from IAR. I have two boards - with STM32F103 and STM32F107. The first one works properly with my code. When I use the second one, my PC (with Win XP) doesn't see any device connected.
I see from documentation, that F103 uses custom USB, whereas F107 uses USB_OTG. Does it change anything in my case? Should I use some other initial code?
I use just 3 pins for USB in this mode: A11 and A12 for RX and TX, and the third out pin, connected to D+ via 1.5K resistance (USB configuration pin). USB_OTG assumes usage of A9 and A10 for VBUS and ID, but are they really needed in the case of Virtual Com port? I did't use them in F103 and assume, that they are also not needed in F107.

The second moment to be reason of error (as I assume), is HSE frequency. On the board with F103 there are 8MHz oscillator. On the board with F107 there are 25MHz. If the first one works properly with my code, how should I change the code for the second board?

Any help will be much appreciated. Thanks in advance!