What to do with USB 3.0 ID pin?

Question

I'm working on a simple front I/O board that connects to a PC motherboard. There is a standard connector in the "Intel Internal Connector And Cable Specification" that give a pin-out table of the internal motherboard connector. I have verified that my motherboard matches this.

The one thing I am confused about at the moment is the purpose and function of the "ID" pin included in the header.

Obviously, this forms part of some overcurrent protection circuit, but I have no idea what I'm supposed to do with it.

Am I just supposed to ground it? Leave it floating? Put some sort of current shunt on it? Have my own over current detection circuit and use this pin to signal over current events?

Answer 1

The Intel documentation is, as always, on top of it. First, there is a brutal discrepancy between the name of pin10, "ID", and attached description as "Over Current Protection". This gives some hint that the pin function is not really defined, and Internet doesn't say much. I can only share two bits of information I have:

1. According to this blog entry an alleged HP employee offers a snipped of Orcad schematics,

where the signal is labeled as "cable detect". Then, in fairly bad English, he talks about POST error if the pin is not grounded, citing:

Pin 10 is detect the front USB 3.0 cable. The cable IO before this PIN, so that the system knows that the cable is installed.

If the 10 pin is connected to the mass, which means that it is the rider to pin 4, 7, 13, or 16, the system will think the cable is installed and it will not be a POST error during startup. The pins are very thin and fragile, so it may need a rare jumper to do so.

This work around is not recommended or supported, as it suggests the system cable is installed, and of course before USB 3.0 ports will not work. As an employee of HP, I must say this. ;-)

Therefore it is possible that HP desktops use this pin as cable detect, although I really see no reason for that.

2. In cables that I have (from eBay), the pin 10 is FLOATING.

So I guess it is up to your particular board what to do with this pin.

Answer 2

So, in the end, I never ended up finding an answer to what the right thing to do here is.

I decided to leave the pin floating and try to bodge a solution in case it went wrong.

It seems that in my setup, the ID pin was not used for anything. I have not noticed any issues with leaving this pin alone.

I'll leave this open so that hopefully a bored Intel engineer will come across the question and give a real answer as to what the right implementation is.

Answer 3

I found this source of information about the ID-pin: Why does micro USB 2.0 have 5 pins, when the A-type only has 4? It seems that this pin is used to distinguish OTG-hosts from slaves. A connection to the GND-pin (i.e. shorting pins 4 and 5 in the micro-usb-connector) signals to the device.