Installing new USB ports - ground required?

Shtanto

Hi all,

I've got a few internal USB headers on my motherboard lying idle. I bought some low cost back plates for them. The motherboard is a GA-P35C-DS3R. So that's USB 2.0, minor detail afaic. A standard USB header takes 5 wires, or 5 header pins. 2 data, 2 power, 1 ground. Thing about USB internal headers is that they only have 9 pins though. So I've got 10 ports on the plug to go into the header but only 9 header pins overall. Thus far, the front USB ports I'm using with the first USB header have always worked fine, even though only 1 of them appears to be grounded. Part of me thinks all USB ports need to have a ground pin wire running to an appropriate header at all times. This ground header is usually black, supposed to be gray but there you go. I suppose the next question is if the USB port does need grounding, could you bridge the pins with a small filament? Or is that a terrible idea?

Thanks,
Eoghan

yoyo

Moved from Comp & Tech

USB 2.0 ports are 4 pin. Power, data x 2, ground.

The 9th pin in a 2-port motherboard header is just there to make sure you don't plug the connector the wrong way around.

Shtanto

I see. You can imagine how confusing it is to see a 5 pin plug which connects to 5 pin headers on 1 side but only 4 on the other. Red at the top, black at the bottom. Is the ground wire ever essential for USB 2.0?

Ground is one of the 4 pins, yes its essential, it wouldn't work without a 0V reference.

The 9th header pin is NC, it doesnt go anywhere. Its sometimes called shield-ground but its optional and doesnt do anything, its just there to provide a one way key. If you only have a single-port connector then you have to be careful to put it the right way around.

Shtanto

I already have one header in use so I'll be able to use that as a reference. What has me muddled is that there are 5 ports on the internal USB connector. This has me looking for a 5 pin header on the board, and sure enough, there are 5 pins on one side, 4 on the other. Only 4 are used for USB 2.0, is that it? I suppose then I don't need to worry about one empty port on a USB header after all. Is it the lower black wire that can be left unconnected?


e.g. device 2 as illustrated will only have 4 connected wires?

Shtanto

Installed now, hope it'll work. 5 ports, but only 4 need connecting? Doesn't seem right somehow.

I have an aquastream XT USB 12V pump as well. There's supposed to be an RPM signal cable. I have it, but I'm not sure what to do with it.

Genghiz Cohen

[CompleteGuess]
Could that 5th pin be a shared ground for the 2 devices?
So 2 power pins and 2 data pins each and a shared ground?
[/CompleteGuess]

Shtanto

Genghiz Cohen wrote: »

[CompleteGuess]
Could that 5th pin be a shared ground for the 2 devices?
So 2 power pins and 2 data pins each and a shared ground?
[/CompleteGuess]

I'm really hoping it is. That way any errant current would 'arc' across the back plate and down the earthing/grounding wire that's already connected. USB isn't much more than 5V at the best of times so I don't think I have much to worry about

The 5th pin on your device connector is shield ground. If you tied it into the ground plane it would turn the cable into an antenna for any EMI that found its way into the ground plane.

As I said already, S-GND is not supposed to go anywhere. Whether it connects to no pin (on the side of the motherboard header that only has 4) or to the NC pin on the other side makes no difference because the NC pin doesnt go anywhere. Its a dummy pin.

Shtanto

I see. So even though there is a side with 5 pins and space for 5 pins, that 5th pin is inert so to speak? Thanks again. Keep reassuring me - I think I already have it wired in correctly. The red wires are all oriented in the same way and as you mentioned earlier, a functional USB port only needs 4 pins to work properly.