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USB problem with recognizing devices

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USB problem

I encounter problem with a USB 1.1 device design. When it is plugged to a particular PC, the device fails to be recognised. Or even at times when it is recognised, it can vanish all in a sudden. The same device works perfectly on all other PCs within scope.

The problem is somehow solved by adding a 100pF capacitor at the DM or DP pin (either will do) to ground. Since i have never seen a schematic of USB that has a de-coupling capacitor at this position, i suspect it is a inherent noise problem caused by the PCB?

Would it be a problem related to layout geometry? Or would it be merely noise-related?

Thanks any advice :)
 

Re: USB problem

Could it be a problem with the USB host controller?
 

Re: USB problem

This PC (the host controller) could be funnier than the others as my device works fine on most other PCs. But other off-the-shelf devices like flash disks also work well on this PC. So i think there is some compatibility issue to improve here.
 

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