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STM32F103 USB_CDC Application Abnormal

Question asked by Quinn Liu on Dec 11, 2017

My question is as follows:

     Use STM32F103RCT6 USB virtual serial port applications (library file: STM32Cube_FW_F1_V1.6.0 library; project file: USB_Device \ CDC_Standalone; compiler tools: Keil uVision5), in the evaluation test, the STM32F103RCT6 connected to the PC via USB (STM32F103RCT6 has been downloaded CDC_Standalone Application software and power-on), and the PC side does not open the corresponding USB virtual serial port. Under normal circumstances, the USB SOF packet should be only 1ms once on the USB bus. But in fact there are a lot of data packets on the USB bus (about 12us a packet), The bus is in an abnormal state! ? Abnormal waveform is as follows:



The correct waveform should be: