stm32 and usb interface

Forum|Forum|9 years ago
May 2, 2017
6 replies
1018 views

Posted on May 02, 2017 at 15:03

I have a problem with usb interface.

Every time that I restart the microcontroller, I must to unplug and replug the usb cable.

Is there a way to reset the usb interface an startup?

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howard n2wx

Associate III

Posted on May 02, 2017 at 15:54

Classic problem. Is USB_DP is pulled up to +5?

Denis GottardelloAuthor

Associate III

Posted on May 02, 2017 at 16:19

Using a multimeter I have 3.3

howard n2wx

Associate III

Posted on May 02, 2017 at 16:23

Thing is, if it's pulled up in hardware you'll need to either power cycle the board or unplug the PC to get it reconnected.

Perhaps consider switching the USB_DP pullup with a GPIO-controlled transistor or FET to signal the need to reinit the USB link.

Andre Webber

Visitor II

Posted on May 04, 2017 at 07:48

I had a similar problem on the STM32F4 series as the DP is pulled up in hardware - on boot-up I set the USB pins as GPIOs and set them low, waited for 100msec and then started the USB Host or Device driver up again which switches the pins to their alternate function for usb. This seemed to force the PC to see the device 'disappear'.