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Design >> High-Speed I/O Design >> USB 2.0 Low Speed Buffer Up/Down Stream Difference
https://designers-guide.org/forum/YaBB.pl?num=1275610250

Message started by neoflash on Jun 3^rd, 2010, 5:10pm

Title: USB 2.0 Low Speed Buffer Up/Down Stream Difference
Post by neoflash on Jun 3^rd, 2010, 5:10pm

Why in USB 2.0 spec, the drive loading capability is different between up and down steam facing ports?

For downstream, it is 200-600pF while for upstream it is 50-150pF?

Title: Re: USB 2.0 Low Speed Buffer Up/Down Stream Difference
Post by casual on Jun 11^th, 2010, 6:14am

It gives more stringent rules to downstream ports (host & HUB) since they have power supply.
While upstream ports normally is a device which get power from host or HUB. So their driving capability is less.

Hopefully it is correct.