For anyone who loves the feel of these Model M "clicky" keyboards, a company called Unicomp purchased the rights and still manufactures them and even has USB versions.<p>I own one and I love it.<p><a href="https://www.pckeyboard.com/" rel="nofollow">https://www.pckeyboard.com/</a>
The high being too low on an open-collector bus is a rather unusual situation, since it's more common when mixing logic families that the pulldowns are too weak to satisfy Vih(min).<p>From the IBM PC/AT schematics we can find that the pullups are on the host side and are 10k, and the Intel 8042 used as the interface controller has a Vih(min) of 2.0V. On newer motherboards, the KBC is usually built into the SuperI/O. As an example, I picked the D845GRG as one listed motherboard that required the modification, and discovered that it has either an SMSC LPC47M172 or NS PC87372. They both specify a Vih(min) of 2.0V, but the datasheet for the former surprisingly recommends a 2.7k(!) pullup for the PS/2 ports. That is surprising because the original IBM PC/AT only needs 10k. Maybe these "non-compliant" motherboards are running the port at a faster clock than the original?
Love the clacky keyboards. Right now I'm typing on a Unicomp "New M" <a href="https://www.pckeyboard.com/page/product/NEW_M" rel="nofollow">https://www.pckeyboard.com/page/product/NEW_M</a><p>They are manufactured by the same company that made the original for IBM (in Tennessee, USA).
I bought a cheap PS/2 to USB adapter off of Amazon to get a Model M working with a modern computer. I wanted it to work on both my PC desktop, which has a PS/2 connector, and my Macbook, which doesn't.<p>The adapter I bought was complete junk and didn't seem to work correctly, but I had some Pro Micros lying around (about $5 a piece) and managed to flash them with the Soarer's Converter firmware. Then I cut the 2 PS/2 connectors off of the cheap adapter and soldered them to the correct pins on the Pro Micros, and I ended up with 2 converter cables that worked just fine.<p>If you want cables that don't look like you built them, you can find Soarer's Converter cables on eBay that look professionally made.
I have two Model M keyboards, the main one (using it right now) and a spare one; needless to say that the spare one is still unused since the main one doesn't want to break after 28 years!
Another possible mod for the keyboard, although purists would possibly not like it, is upgrading the controller board so that it speaks directly USB. Here are some pages I found on the subject:<p><a href="https://github.com/mschwingen/hardware/tree/master/modelm-usb" rel="nofollow">https://github.com/mschwingen/hardware/tree/master/modelm-us...</a><p><a href="https://blog.lmorchard.com/2016/02/21/modelm-controller/" rel="nofollow">https://blog.lmorchard.com/2016/02/21/modelm-controller/</a><p><a href="https://www.crackedthecode.co/how-to-supercharge-your-ibm-model-m-with-qmk/" rel="nofollow">https://www.crackedthecode.co/how-to-supercharge-your-ibm-mo...</a>
> Another relevant factor is that the older technology used on the IBM keyboard's controller PCB requires more power to operate than newer keyboards.<p>I ran into this problem with my original Model M. All the PS/2 to USB converters I bought (even the blue square one quoted in the article as working) were borderline and they would sooner or later lock up and require a reboot (you really shouldn't hot-plug a PS/2 keyboard, as some machines have a fuse soldered on their board).<p>I have not tried any of the new keyboards sold by Unicomp (I had one in the past), but I see their newest version of the Model M has a USB interface and presumably it's reliable.
I have an old keyboard (2 of them actually) since 92-93 I think. They look exactly like the one on the picture. Both work perfectly and do not require any modifications with the modern computers. One is permanently hooked up to a main server and being used very rarely when updating hardware. Another being dragged around as a spare. I would still use those as my main but after playing with ergonomic keyboards few years ego I got hooked and now use only those for every day work.
Very good to know.<p>Without any technical knowledge (not at the level of the author of the article) and in my little experience, I can confirm the issue about the long cable not working and the short one working, it happened to me a few times, but in my ignorance, I thought only "ha! the cable is too long and there must be some voltage drops/internal resistance issue", never thought of the possibility of adding resistors (that does sound counter-intuitive, at least to me).
Why is a comment saying this post should be tagged (200x) dead? This post is from circa 2005 as the update date says (or even older) and if there were electrical issues with motherboards over 15 years ago, I can imagine now. Also, it has passed the same time since the blog post as from the original keyboard being manufactured and the post being written (1990..2005, 2005..2021). So, it's pretty important to specify that in the title.
I would be more impressed if they had showed how to convert a USB keyboard to PS/2. That's very rare, while solutions for connecting a PS/2 keyboard to a USB port are relatively commonplace.