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Impossible Early USB Headers.... Help?

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Coatchawa

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Jul 2, 2010
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I have this old AT computer. I would like to get the onboard USB working, but there's one problem. This motherboard has non-standard USB headers, and I can't figure out the correct wiring for them. There are two rows of five pins.
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Here's what I've found out: Pins 1-5 are USB1, and pins 6-0 are USB2. When VOLAGE is hooked to PIN1 and GROUND is hooked to PIN4, I am able to power devices such as an optical mouse.

I would like to figure this out through trial and error, but I have found out the hard way that this will mess up USB devices. I've ruined a 2gb flash drive and a card reader from trying to figure this out.

Does anybody have any ideas on this? I've searched long and hard to find information on this, but all I've found is a flimsy manual for the board that doesn't tell what the pins are for.

Any help/input is appriciated.
 
Here's what I have from an old PM-8600 board:

Pins 1,2 = +5VDC
Pins 3,4 = USB Data -
Pins 5,6 = USB Data +
Pins 7,8,9,10 = Gnd.

I can verify that these are correct for my board.
 
Chuck(G) said:
Here's what I have from an old PM-8600 board:

Pins 1,2 = +5VDC
Pins 3,4 = USB Data -
Pins 5,6 = USB Data +
Pins 7,8,9,10 = Gnd.

I can verify that these are correct for my board.
Click to expand...
No guarantees of course, but I don't think internal USB connectors are totally "non-standard"; some MBs do have one or two pins missing among 7-10 as a key, but the sequence is usually the same as the USB port itself (like Chuck's).

The OP's numbering is non-standard though; as in Chuck's example, dual-row headers are usually numbered odd along one side and even along the other. As usual, a model number would be helpful; I don't think any ATs came with on-board USB... ;-)
 
Last edited:
Mike, I hope that the original poster means "AT" in the sense of "not ATX". ISTR that USB "A" side cables with 5-position header connectors mounted on a bracket were pretty standard fare in pre-ATX days.

ATX was supposed to fix all of the problems with nonstandard connector positions and whatnot. Now, you need a bucket full of backshields and hope that at least one of them works with both your board and the case you're trying to fit it in...
 
It would help to know what model and brand of motherboard.

If the motherboard dates from 1996, the USB ports most likely won't work no matter what you try and likely fry whatever gets plugged in. Manufacturers tried to anticipate the spec and a few mistakes were made along the way.
 
I skipped a few posts, but in my experience USB headers have the following pinout:

1 2 3 4 5
6 7 8 9 0

where 5 and 0 are usually not connected or there's just no pin at all.

I just wrestled with this like a week ago, but I don't have the notes anymore on what pins do what. There's a +5V, Data +, Data -, and Ground for each row, but you'll need the order.

I think Chuck is describing it in the following layout:

1 3 5 7 9
2 4 6 8 0

So to translate his mapping into mine (and the OP's):

1&6=+5V
2&7=Data -
3&8=Data +
4&9=Ground
5&0=Key/Unused

Chuck didn't specifically mark Key/Unused, but in my experience it's always the far right two pins. All AT boards w/ onboard USB and all ATX boards I've had to plug wire-by-wire USB cables into have followed that keying.

Edit: Oh, and I forgot to mention. Modern USB brackets and case ports always have one pin filled in on the connector. If you're in a situation where the motherboard has all 10 pins, and your connector has 9 (usually pin 0 is filled in), just bend the offending pin on the motherboard - it works fine (I've done this) as it's only an extra ground or unused pin and isn't necessary. Make sure you have the connector plugged in the right way though, as with that kind of situation you could end up bending the opposite pin and plugging it in backwards, screwing up any devices, the motherboard (or at least USB chips), and the bracket/case.
 
Raven said:
Chuck didn't specifically mark Key/Unused, but in my experience it's always the far right two pins. All AT boards w/ onboard USB and all ATX boards I've had to plug wire-by-wire USB cables into have followed that keying.
Click to expand...

Yes, it's standard 0.100" spacing dual-row 10-pin header. But keying on these was far from universal--I've seen no keying, keying on pins 7 and/or 8, etc. Thankfully, the ordering of the signals appears to be the same.
 
Chuck(G) said:
Yes, it's standard 0.100" spacing dual-row 10-pin header. But keying on these was far from universal--I've seen no keying, keying on pins 7 and/or 8, etc. Thankfully, the ordering of the signals appears to be the same.
Click to expand...

The keying wasn't standard *then* but afaik it's always the last two pins that are either key, spare grounds, or completely missing - and now it's always pin 0 that's missing and pin 9 that's key. All of the older USB headers I've seen have all 10 pins but the last two just do nothing important (probably grounds or NC), so I bend them to allow modern brackets to hook up, and they function just fine this way (my Voodoo box has a modern USB header in it in this scenario).

I suppose it's possible that there are boards out there with the signal pins to the right and the spare pins to the left, but I've yet to see one. If, as you say, there are boards that actually make use of pins 9 and 0, I suppose I've just been lucky.
 
It's pin 10, not "0".

A quick check among three motherboards of the P1 era shows:
  • No keying--all 10 pins present.
  • Pin 10 used as key
  • Single-row USB header of 5 pins, with the 4th pin missing.

Draw your own conclusions.
 
So typically it seems that what I said is correct, but there are boards with variations on the USB header so it's not foolproof.

Most likely whenever you see all ten pins or the bottom right pin missing, you're dealing with the modern style of USB. As for other configurations, it's hard to say and may vary from motherboard to motherboard or manufacturer to manufacturer.

^--- My Conclusions have been Drawn. :D

BTW: I was calling the last pin "0" because that's what the OP called it and I wanted to avoid confusing him. In retrospect though it is nice to have a single digit when drawing ASCII pin diagrams..
 
yes, all of my older motherboards of the early USB variety are also the same as described. i've come across some very strange PS/2 mouse pin headers though.
 
Something I've yet to see mentioned here, but highly relevant and very important: the "unused" pins aren't always ground. I've got (or had, not sure where it is) one board where it's actually +5V.

Because the pin is technically 'unused', the motherboard manual will usually not tell you what the pin does.

If the connector for the ports has an additional ground wire in the unused pin position, remove that pin from the connector as a precaution. Bad things happen when that pin is +5V and the USB port assembly connects all the "grounds" together...
 
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