The next step are the passives on the data lines. The PIIX3 datasheet indicates that there should be a 15k pulldown on the USB port side, a 27 ohm series terminator near the PIIX3, and a 47pF filter capacitor on the PIIX3 side of the series terminator. Tracing out the signals leads to this collection of unpopulated components on the back of the motherboard near the PIIX3:

It's pretty clear here by probing or even just taking a look at the traces which are which. They are 0805 or maybe 1206 footprints but rather than ordering some fresh components, I just used what's in my component drawers which include 0603's and 0402's. They look a bit wonky, but hey, it's the back of the board.

And the last bit is the 48MHz USBCLK. Depending on how this is hooked up, there may be some termination passives to populate. Probing around should let you know what you are dealing with. In my case, R101 and C63 form an AC terminator adjacent to where the clock signal hooks up to the PIIX3:

There's no hard and fast rule on these. There's a PCICLK nearby that's also terminated with an AC terminator with the resistor being 330 ohms. The capacitor is impossible to measure without depopulating it. There's a few rules of thumb out there for picking a capacitor value using the signal rise time and the trace impedance. The signal rise time is 1.2ns, and the impedance is whatever my best guess is. The exact value isn't super critical here. It's only 48MHz after all. I went with 47pF because I already had them out, and 270 ohm on the resistor because it's what I had in 0603.

Good to go. BIOS support for programming the chipset may be necessary and of course appropriate OS drivers are necessary as well. Without BIOS support it may be possible to poke the right register values early in the boot sequence to get things going. In my case, I needed to update my BIOS revision to get things working.

Great work!

If you wanted more than 2 ports you may have been able to put in a pin header 😀 or so that you did and use an adapter.

Re: Adding more usb ports to old motherboards without using a card

almost a few years late on this but regarding USB support on motherboards with Intel PIIX3 chipset, read the following article from the Wims Bios site:

Wims BIOS - Why is there no option to enable USB in my BIOS setup?

and this old forum topic from sysopt.com - USB on a i430VX

Locate the Intel chip 82C371SB and see if it's an "SU052" or "SU093" revision. The latter has working USB ports that follow the UHCI 1.0 specification, while the former does not.

erpster-xg4 wrote on 2024-08-20, 02:48:

almost a few years late on this but regarding USB support on motherboards with Intel PIIX3 chipset, read the following article f […]
Show full quote

almost a few years late on this but regarding USB support on motherboards with Intel PIIX3 chipset, read the following article from the Wims Bios site:

Wims BIOS - Why is there no option to enable USB in my BIOS setup?

and this old forum topic from sysopt.com - USB on a i430VX

Locate the Intel chip 82C371SB and see if it's an "SU052" or "SU093" revision. The latter has working USB ports that follow the UHCI 1.0 specification, while the former does not.

This is good to know. Some months back we had a thread about which motherboard was the first to have working USB - I knew that there were VX chipset motherboards that had working USB, and there were also ones that even went as far as having the pins on the motherboard, but the manual said that they did not have working USB ports. I knew it had to be down to a revision of the chipset, but I didn't know the actual alpha numeric designation. My PCChips M520 (430VX) must have the SU093 revision as it does have working USB ports.

Interestingly my Packard Bell PB810 motherboard has the SU093 variant and can verify the two onboard USB ports definitely do work. However the strange thing was, when I originally got the motherboard the USB ports were completely hidden behind the original rear metal backplate. I'm not sure why they would have done that. If they weren't confident in the reliability or something, why populate them in the first place?

That's an OEM motherboard from Intel. Packard Bell probably just bought whatever was available at the time for their PCs, without updating their model listing.

mscdex wrote on 2024-08-21, 12:34:

Interestingly my Packard Bell PB810 motherboard has the SU093 variant and can verify the two onboard USB ports definitely do work. However the strange thing was, when I originally got the motherboard the USB ports were completely hidden behind the original rear metal backplate. I'm not sure why they would have done that. If they weren't confident in the reliability or something, why populate them in the first place?

Do you know the release date of that computer? A quick look at the Win95 Wikipedia page indicates the first USB support was released in August of 1997. My hunch is that this is likely a year after the computer was on the market. My speculation: I can imagine a lot of support headaches caused by having these ports exposed when they do not yet work and they had no idea when they would.

Repo Man11 wrote on 2024-08-21, 15:41:

Do you know the release date of that computer?

No idea, I'm not even sure exactly what models it would have been used in. I was only given the motherboard, audio daughterboard, and riser.

Based on the chips though the latest date code I can find is 33rd week of 97.

mscdex wrote on 2024-08-21, 16:18:

Repo Man11 wrote on 2024-08-21, 15:41:

Do you know the release date of that computer?

No idea, I'm not even sure exactly what models it would have been used in. I was only given the motherboard, audio daughterboard, and riser.

Based on the chips though the latest date code I can find is 33rd week of 97.

The first BIOS date for the PCChips M520 is late August of 1996 (correction, it was actually 7-2-1996); presumably this would have had the VX revision without working USB. Probably your Packard Bell was similarly released with a motherboard version without working USB and a later revision that had it. Looking at the (admittedly sparse) notes for BIOS updates for the M520 I never saw any mention of separate BIOS updates for revision with/without working USB ports so I suppose the later BIOS updates for the later revisions of the motherboard didn't cause any issues for the earlier versions.