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Hi,
I have some troubles using the usb interface fromt he STM32F103 processor; if the processor is connected by a usb cable to my computer x86, then I didn't receive a start-of-frame.
Using the oscilloscope, I can see that only at startup of my computer (x86), there's some communication. After that only the reset impulse will be transmitted - nothing else. Is this behaviour normal, or should usb try to send a SOF as long as the host will get the device usb datas?
How will a SOF frame look like? so that I can see if it will be transmit at startup?
I also tried to use the files (keil project) from the evaluation board STM32 - the same behaviour...
best regards Jan
maybe I found my error:
I've installed a pullup 1.5k resistor on the D+ line (to 3V3); the device is always on when the host controller is also on -> both controllers use the same power supply. Maybe the STM32 processor is too slow to recognize the first SOF frame because the init takes too long...
Are there any recommendations? Is it better to connect the 1.5k pullup resistor directly to a GPIO with an additional 47k pulldown resistor. And pulldown the GPIO during the init?
Jan