I am designing a development board for STM32F103 microcontroller. I plan to implement an on-board USB for interfacing with the uC. I referred a few designs online and have always found some pull up logic on the D+ line.
Can someone please explain me the use of the pull-up logic and also tell me whether the 22R resistors are necessary or not.
Best Answer
http://www.beyondlogic.org/usbnutshell/usb2.shtml
The series resistance are for line termination
http://www.semtech.com/images/datasheet/usb%20line%20termination%20_ag.pdf