USB D+ D- identification

[electr_peter]

Hi,

I have laptop with weird USB connector and I plan to add standard connector. I presume USB port functions well, but I do not know exact pin out. 5V and GND is known.
Is there a way to discriminate between D+ and D- pins just by checking voltages? Or is it a question of functional test?

[wraper]

Hi,

I have laptop with weird USB connector and I plan to add standard connector.

What is weird in it? Why would you want to add "standard" connector. Are you sure that it is USB at all?

[wraper]

As a guess, "weird USB" could be 4 pin IEEE 1394 (firewire) considering the same pin count.
http://en.wikipedia.org/wiki/IEEE_1394

[SL4P]

--- or HDMI / DisplayPort ?

[electr_peter]

USB connection is on the LCD display of ThinkPad X2x series. It is definitely USB (manual and available adapters (cameras, mics) confirms it. There also was simple USB adapter for these devices). Official name is "ThinkPad UltraPort".

[SL4P]

My X220T has USB & USB 2.0 - and a mini-displayport connector...

[Rasz]

If you can plug a usb device in, and it works, then it could be a powered esata port.

wait what? rethink that statement

[PA0PBZ]

http://www.thinkwiki.org/wiki/UltraPort

[rs20]

People, the OP is asking how to disambiguate between D- and D+. If you've got two wires in your hand, D+ and D-, and you don't know which one's which, how do you figure it out?

I think the easiest way is to just try plugging a device in. I'm pretty sure it's safe to do because it's a differential line, so the 1's and 0's will be backwards, no risk of bad things happening (like if you were to get the power and ground backwards).

[PA0PBZ]

People, the OP is asking how to disambiguate between D- and D+.

I know, but he's trying to figure this out for an Ultraport. The link I posted shows the connections:

[Rasz]

If you can plug a usb device in, and it works, then it could be a powered esata port.

wait what? rethink that statement

Powered esata is literally a combination of USB2.0 and ESATA. The center is a plastic USB connector, and the perimeter pins are for ESATA.

wtf

[zapta]

If you can plug a usb device in, and it works, then it could be a powered esata port.

wait what? rethink that statement

Powered esata is literally a combination of USB2.0 and ESATA. The center is a plastic USB connector, and the perimeter pins are for ESATA.

wtf

http://en.wikipedia.org/wiki/ESATAp

[Rasz]

http://en.wikipedia.org/wiki/ESATAp

yes, I was the one eating it

[electr_peter]

Thanks for replies, linked schematic seems to match pinout.

As for D+ and D- differentiation on host side, it looks impossible to do just by electronic characteristics. Device pulls one of the lines high/low to indicate speed, host just presents differential line.

[Lukas]

I'm wondering why USB isn't capable of swapping D+/D- when necessary, would make PCB layout easier. Newer serial interfaces like PCIe automatically handle polarity inversion.

[rs20]

I'm wondering why USB isn't capable of swapping D+/D- when necessary, would make PCB layout easier. Newer serial interfaces like PCIe automatically handle polarity inversion.

PCIe also handles crazy stuff like deskewing between different pairs, etc. So once you've got all that processing and buffering in place, adding a not gate is clearly not that difficult comparatively. Also, making PCB layout easier is genuinely an actual issue when you're routing 16 pairs or more. That seems legitimately useful somehow.

USB, however, is much simpler and designed to be cheap to implement? Flipping the two lines is just a single via, it doesn't seem that bad. I dunno, I'm just making stuff up here.