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[Solved] USB device not enumerated

Question asked by Václav on Aug 1, 2014
Latest reply on Aug 6, 2014 by Václav
Hello,
I'm trying to get the USB Virtual COM port loopback example project work on STM32F102.
When the USB is connected, the PC says "Unkown device connected" with VID 0 PID 0 so obviously it's not enumerated.
On the MCU side, it detects that the USB was attached, but goes to suspend state after 2 seconds or so. The device state is "ATTACHED", doesn't ever get to CONFIGURED.

It should be software problem because the hardware looks ok. I have 33 ohm series resistors on DP and DM lines, 1,5k pullup on DP, and VBUS wired to PortA 9 through a 10k resistor.
The system and usb clock setup also look good.

What could cause the device not enumerate and the device entering suspend mode when connected (no communication)?

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