why USB3 motherbard headers have so many unused pins?

4

While researching how to use my new motherboard with a 20pin USB3 header with my USB2 cables (so i wouldn't have to wait for yet another delivery), the farther i could go was this image

enter image description here

if i understand this correctly, the 20pin header has for each USB3 port:

  • TX (D+ in pic)
  • RX (D- in pic)
  • GND x2
  • extra_TX+
  • extra_TX-
  • extra_RX+
  • extra_RX-
  • +5V

plus a shared ID pin.

the older USB2 header, had for each port:

  • +5V+
  • TX
  • RX
  • GND

the USB2 maps 1:1 to the final usb port... but the USB3 for me is just crazy! and I really doubt if I crack open a chinese USB3 20pin cable i will find much more than just a wire going from a few select 4 pins...

The question is: Why does it have all those pins if the ultimate connector only have 4 pins anyway?

Edit: ok, apparently i missed a pic on wikipedia that cames with no explanation besides the pinout, that hints we will have a (as far as i can tell from the pic, idiotic) 10pin wide full-USB3 connector at some point...
http://en.wikipedia.org/wiki/Universal_Serial_Bus#Physical_appearance

enter image description here

So, new question, is it safe to just use the 4 pins that the current usb ports use from the 20pin header? as the original question stands: the ultimate connector going out of the case only has 4 pins... why do i need to connect more on the internal plug if they are just going to be forever unused?

gcb

Posted 2012-12-18T00:13:07.797

Reputation: 3 392

Question was closed 2012-12-18T12:51:01.773

Huh? USB 3.0 has 4 extra data lines. – Breakthrough – 2012-12-18T00:21:51.333

Using only 4 pins will limit it to USB 2.0. That is why USB 3.0 is backwards compatible. – Fiasco Labs – 2012-12-18T00:52:39.413

You shouldn't edit your question to ask another question. If you've found the answer, then answer it your self. If you have another question then ask it, instead of editing your question as a new one. – James Mertz – 2012-12-18T01:52:01.280

The 20 pin header is for two USB3 ports. One port down the left side and the other down the right side. – Brian – 2013-01-02T04:10:18.957

Answers

5

The final connector does not have 4 pins, it has 9

http://pinoutsguide.com/connectors/usb_3_plug.gif

Now, it is electrically backward compatible with the old 4 pin connector of the 2.0 and lower USB, but a "real" USB3 port will have 9 pins on it (and be blue, the color is part of the spec).

Ok, correction about the color. Per 3.1.1.1 of the USB Spec

As an aid to users, USB 3.0 mandates standard coloring for plastic portions of USB 3.0 plugs and receptacles.

However later on in 5.2.1.1 it states

A unique color coding is recommended for the USB 3.0 Standard-A connector plastic housings to help users distinguish the USB 3.0 Standard-A connector from the USB 2.0 Standard-A connector (refer to Section 5.3.1.3 for details).

Then in 5.3.1.3

Since both the USB 2.0 Standard-A and USB 3.0 Standard-A receptacles may co-exist on a host, color coding is recommended for the USB 3.0 Standard-A connector (receptacle and plug) housings to help users distinguish it from the USB 2.0 Standard-A connector.

Blue (Pantone 300C) is the recommended color for the USB 3.0 Standard-A receptacle and plug plastic housings. When the recommended color is used, connector manufacturers and system integrators should make sure that the blue-colored receptacle housing is visible to users. Figure 5-5 illustrates the color coding recommendation for the USB 3.0 Standard-A connector.

enter image description here

So it says you are required to color all of your usb 3.0 ports the same and it "recommends" coloring 2.0 and 3.0 on the same machine different colors and you use Blue (Pantone 300C) for the color of the 3.0 ports, that is not required.

Scott Chamberlain

Posted 2012-12-18T00:13:07.797

Reputation: 28 923

"and be blue, the color is part of the spec" - All USB ports on Macs that supports USB 3 are USB 3 capable and do not have blue inserts. – Karan – 2012-12-18T02:42:30.390

thanks for the link. but hey, my motherboad (gigabyte z77mx-d3h) and several others i inspected when buying, had blue USB3 ports, all with 4 pins. Same with my Verbatim usb3 flash drive, which gets me 97Mbp/s when connected to those blue ports. – gcb – 2012-12-18T07:59:33.357

So the rectangle image on wikipedia is just crazy talk? having the extra pins on top makes more sense... – gcb – 2012-12-18T08:03:23.087

1@gcp I added some quotes from the USB spec, I recommend downloading the zip and flipping through the spec, its not that hard to read and it will answer any of the questions you have about how the cabling works. – Scott Chamberlain – 2012-12-18T08:27:31.633

Also the image you included from the wikipedia page, that is the USB 3.0 Micro-connector (section 5.3.4 from the spec pdf). – Scott Chamberlain – 2012-12-18T08:31:23.717

4Trust Apple to try and be different – deed02392 – 2012-12-18T08:39:12.237

i'm downloading the 22mb pdf... really want to understand where the extra 5pins will play out, as nothing USB3 nowadays has more than 4 pins. – gcb – 2013-01-09T05:36:00.027

Ok! finally understood it! the USB3-A connector does have 9 pins. but the new 5 are hidden behind and in between the regular 4 pins! can't believe it took me this long to notice that. So the answer to the quesiton is NO. they are not unused. – gcb – 2013-01-09T05:54:09.963

Asked: 2012-12-18T00:13:07.797

Viewed: 8 795 times

Active: 2015-09-24T08:09:42.303