2014-05-26 16:10 GMT+02:00 Luke Kenneth Casson Leighton <lkcl@lkcl.net>:

On Mon, May 26, 2014 at 3:04 PM, mike.valk@gmail.com
<mike.valk@gmail.com> wrote:

> That means that every USB3, slave, device must accept a USB1/2 link,
> from a master,

yyyup.

> USB3 requires 5 extra pins

4 coming off the CPU Card. what's the 5th one?

Apparently: GND_DRAIN: Ground for signal return

http://en.wikipedia.org/wiki/USB_3.0#Pinouts

Probably it used to "drain" signal leakage from the SuperSpeed cable pairs. But how that is to be terminated on the devices properly, I have no idea. I'm not sure if it's necessary in the EOMA connector either.

Couldn't find anything useful on the Internet either.

http://electronics.stackexchange.com/questions/107669/usb3-with-fewer-wires

Just a notice in this one:
http://www.onsemi.com/pub_link/Collateral/AND9114-D.PDF

Page 7: Quote on PCB design:
"Place grounds between high speed pairs and keep as
much distance between pairs as possible to reduce
crosstalk"

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