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stm32f407zg usb problem

Question asked by Wasilewski.Piotr on Feb 24, 2016
Hello!

I have a strange problem with the mass storage usb on stm32407ZGt6. Why is it odd ? That's because the same code works on stm32f407ZEt6 just fine. I thought that these cpu's differ only in the amount of flash memory, but clearly there is something else. I have checked the following things: 

-CPU clocks ( the registers are the same in both cpu's) 
-The voltage ( I added extra capacitors)
-the crystal - 16 mhz working well 
-electrical connections 
-D+ D- are not swapped or anything like this, the 1,5 k resistor on D+ does not make it work.
-the code is exactly the same

But still on the device with 407zGt6 the PC shows a sign "unknown device", and on 407zEt6 works as it should. 

So I decided to sniff the signals with the logic analyser. this is what I've noticed: (3 pics different zoom ( top 2 signals are from the not working one ) :
help_usb.jpgusb%20help.jpgusb%20help2.jpg

It looks like the "ZG" vesion is faster than the other, but the RCC registers are the same.  What else worries me is the first line ( D+). It differs from working device's D+, but I dont know why. Also the USB registers are the same, besides the amount of frames sent. 

I don't know what may be wrong. The paths on the pcb are just a bit longer, and that's the only physical difference that I'm able to spot. 

Hope You can help me! 

Greetongs,
Peter




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