-1

I want to design a USB hub 3.0 with only D- and D+ data pins (So I wont implement the USB 3 functionality). I chose CYUSB3328 IC for this job.

(The reason I do not use a USB 2.0 for this, is because I could not find USB 2.0 Super Speed with more than four Ports. Plus, I might need the extra power USB 3.0 supplies)

So I started checking if it is actually possible: to not use the TX, RX pins on a USB 3.0 IC.

From this answer I understand that I can only wire that D+ and D- pins, and it will drop to USB 2.0 speed, but I am not happy from that reply, as the question was more general: "reducing the wires of a USB 3.0 wire to make it thinner".

So the question is: To make only D+/D- USB connector communication, do I only need to wire the D+ and D- pins of the IC, and leave the Rx, TX pins floating on both Downstream and upstream sides?

Pictures from the datasheet for upstream/downstream ports pin descriptions:

Upstream:

Upstream

Downstream for Port 1 (all other Downstream ports are the same):

Downstream CYUSB3328

So my end result will be this:

schematic

simulate this circuit – Schematic created using CircuitLab

Will the above schematic connection allow me to use only the D- and D+ pins to communicate, or Do I actually need to use a USB 2.0 for this?

Christianidis Vasileios
  • 2,645
  • 2
  • 9
  • 32
  • 1
    I'm confused. You write about only using D+ & D-, but then in your snapshots from the CYUSB33xx manual you've crossed those pins out and say you're not using USB2 ... Which is it? Either you're using D+/D- and therefore you're using USB2 or you're not using D+/D- and therefore you must be using the TX/RX pairs for USB3. – brhans Sep 22 '21 at 13:45
  • 3
    There's also (afaik) no such thing as "USB 2.0 Super Speed". "Super Speed" is a USB 3 feature. USB 2 only goes up to "High Speed" 480Mbps. – brhans Sep 22 '21 at 13:50
  • @brhans Oh so these "D+ and D-" that I crossed out, I am supposed to use them? I was thinking that some of these "US_RXP, US_TXM" would be used as D+ and D- instead! To your second comment: hm.. How come some USB laptops have 'SS' when using USB 2.0 ports? – Christianidis Vasileios Sep 22 '21 at 13:53
  • The D+ & D- lines are the bidirectional pair used for USB1 & USB2 Low/Full/High-Speed communication. The TX+/- and RX+/- are the unidirectional pairs used for USB3 Super-Speed communication. What makes you think that any particular laptop has a USB2 port labelled 'SS'? I've seen laptops with a mix of USB2 and USB3 ports where the USB3 ports are labelled with 'SS' and the USB2 ports are not... – brhans Sep 22 '21 at 13:57
  • Okay I think I get it better now. My laptop has a port labeled "SS", but has only 2 data lines. That is what I want to do. SS speed with two data lines. So, my laptop uses USB 3.X with Tx+ and Rx+ on these two data lines? (and possibly having the Tx-/Rx- connected together to GND – Christianidis Vasileios Sep 22 '21 at 14:02
  • 4
    No it doesn't - that's not how USB3 Super-Speed works. 2 Lines means USB2 High-Speed is the fastest that port will go. If it claims USB3 SS, then it must have the additional TX & RX pairs. – brhans Sep 22 '21 at 14:07
  • 1
    @ChristianidisVasileios: Are you confusing USB 3.0 Type A connector with USB 3.1-3.2 Type C connector, and thinking the first has only D+/D-? That's not correct. A Type A USB 3.0 connector doesn't have the extra copy of TX/RX pairs that make the connector reversible... but it does have the first copy of TX/RX in addition to D+/D- – Ben Voigt Sep 22 '21 at 14:56
  • 1
    Digikey has USB 2 hub controllers with more than 4 ports in stock, so the whole premise of this question seems wrong. If you only need USB2, buy a USB2 controller. – user1850479 Sep 22 '21 at 16:47
  • @user1850479 the comments and answers here helped me understand the usb 2.0/3.X hubs better. The question is overall helpful. – Christianidis Vasileios Sep 23 '21 at 08:11

2 Answers2

3

Here's a quick overview of USB speeds and standards:

Speed Data Rate USB Standard Required data lines
Low speed 1.5 Mbit/s USB 1.0 and higher D+/D-
Full speed 12 Mbit/s USB 1.0 and higher D+/D-
High speed 480 Mbit/s USB 2.0 and higher D+/D-
SuperSpeed 5 Gbit/s USB 3.0 and higher D+/D-, SSRX+/SSRX-, SSTX+/SSTX-
SuperSpeed+ 10 Gbit/s USB 3.1 and higher D+/D-, SSRX+/SSRX-, SSTX+/SSTX-

There is also USB 3.2 and 4.0, which have been omitted for simplicity.

As you can see, you are restricted to High speed if you only connect the D+ and D- data lines.

For SuperSpeed, you need to connect the two additional data pairs and you need different USB receptacles (see Receptacle (socket) identification for details). Either:

  • SuperSpeed version of Type-A (usually colored in blue) with 9 contacts
  • SuperSpeed version of Micro A (which looks like a Micro A receptacle with an extension)
  • Type-C receptacle

Your PC most likely has a SuperSpeed Type-A receptacle, which has 4 contacts in the front and 5 additional ones that are difficult to spot.

Thus, the main question is not how to connect the CYUSB3328 but rather whether USB high speed is sufficient for your application.

Codo
  • 2,038
  • 8
  • 14
  • *Your PC most likely has a SuperSpeed Type-A receptacle, which has 4 contacts in the front and 5 additional ones that are difficult to spot* Yes thats it, Makes sense now! – Christianidis Vasileios Sep 22 '21 at 16:24
0

This is what I will try, based on your comments and @Codo's answer:

Just like my Laptop has, a USB 3.0 port which is like that:

SS usb

Image source

The 5 pins were hard to spot, so I could not see that this 9-pin connector was there, and it can accept both 9-pin (usb 3) connections and USB 2.0 connections.

So this is the kind of connector I want to make!

I will come back with the results, thank you all.

Christianidis Vasileios
  • 2,645
  • 2
  • 9
  • 32