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USB device disconnect and connect in STM32L0

Question asked by truong.kevin on Dec 29, 2014
Latest reply on Dec 30, 2014 by Chinzei.Tsuneo
I just begin in STM32L0. I using my board for dev an USB example base STM32L053R8. 
And I have a confused about USB connect and disconnect.  I run a test case based on STM32L053R8_NUCLEO_USB for test. And I don't want USB host detect USB device till I call function USBD_Start at the code below. But the Host still detect my USB device. I have check the bit DPPU (BCDR register). It is still disable. I can not Image what is the reason 

  /* Init Device Library */
  USBD_Init(&USBD_Device, &HID_Desc, 0);
  /* Register the HID class */
  USBD_RegisterClass(&USBD_Device, &USBD_HID);
     while (1); 
  /* Start Device Process */

Thank for help.