IBM PS/2 Keyboard Modification | Hacker News Reader

IBM PS/2 Keyboard Modification

ardent-tool.com

89 pointsgrae_QED50 comments

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.

I own one and I love it.

https://www.pckeyboard.com/

How is the durability compared to OG Model M keyboards? I've been seeing Unicomps on eBay come up for around $50. If they are as rock solid as their predecessors, it should be an absolute deal.

Physically, the same.

Electrically, not perfect (but I don't know what the old ones were like). I have a USB one that simply died when I lost power one day. I was astounded to find that it was the keyboard that actually died and not the USB port stopped working or something.

The most reliable keyboards I've found to actually be basic Keytronic models.

I bought one of the Unicomp Model M keyboards in the 101 key configuration for comparison. Build quality is good, not great. Feels similar but is louder and the keys wobble slightly compared to my 89 model m.

If you want this experience, I’d suggest you grab a used model M on eBay. TFI had good reference on usb to ps2 adapters that work. For an xt cable, you can buy a sorros (sp?) converter for 40 bucks. Or a new usb to RJ cable that will plug directly into the keyboard.

One of the most useless purchases of my life.

I bought an endura pro, the ultra-nav (the red nub in the middle of the keyboard) doesn't work properly: it moves at different speeds depending on whether you're moving towards the right vs left. It drives me crazy.

The problem seems to be that it gets stopped by a key and doesn't get tilted enought to trigger pointer acceleration.

I'm supposed to erode a key somehow... To allow the lever to move a bit more, but it's a dumb solution to a problem that shouldn't be there in the first place.

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).

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?

PS/2 is clocked by the keyboard.

PS/2 is a two way protocol. If Keyboard sends data it, then it controls the clock. If Host sends data then it will take care of the clock signal.

From my limited electronics experiencence, you need a pull-up resistors when connecting TTL ICs to CMOS ICs.

It is two way, but the clock is always provided by the keyboard.

PS/2 devices all have pull-up resistors as the only thing driving the lines high are those resistors.

The mcu on either side only ever pull it low and never high.

http://www.lucadavidian.com/2017/11/15/interfacing-ps2-keybo...

Then perhaps IBM's keyboards somehow push the clock closer to the limit (16.7kHz, I believe) than motherboards' controllers can handle? Unfortunately I wasn't able to find any measurements of different keyboards' clock frequencies.

Love the clacky keyboards. Right now I'm typing on a Unicomp "New M" https://www.pckeyboard.com/page/product/NEW_M

They are manufactured by the same company that made the original for IBM (in Tennessee, USA).

It's ridiculous how they don't position the Alt and Win keys properly. That's the only thing holding me from buying one.

You can configure it to be a 103 key with long space bar (it's under chassis style). That's more or less a normal layout, I think.

Same here. I have an older Unicomp that I would like to replace, but I haven't done it for exactly this reason.

Also typing on a "New M"!

I was worried as many reviewers claimed they were slightly worse than real Model Ms but I have to say, I think they got everything down. (I've used an SSK and Lexmark Model M for reference.)

Hasn't the tooling at the factory worn down to the point where you can't get but crap build quality on those Unicomps? Or have they updated the tooling?

They updated the tooling in 2020 for the "new M" keyboards. One in the classic layout and one modeled after the original space saver keyboard (which Unicomp never had the tooling for).

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.

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.

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 one of those cables and it is perfect.

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:

https://github.com/mschwingen/hardware/tree/master/modelm-us...

https://blog.lmorchard.com/2016/02/21/modelm-controller/

https://www.crackedthecode.co/how-to-supercharge-your-ibm-mo...

This is the authoritative source of the most-widely-used mod: https://deskthority.net/viewtopic.php?f=7&t=2510&start=

hey just a heads up, your account is shadow banned

What does that mean?

Wow that's a lot of [dead] comments. I can't even scroll back to the start of them!

This commenter says it started in 2015 (I assume that's accurate),

https://news.ycombinator.com/item?id=27191052

>"Hey @PostThisTooFast, you seem to be shadowbanned based on two flagged comments when your account was new in 2015. Hey @dang, this account has made many good comments since then."

To anyone confused by this thread, look at the "showdead=[yes|no]" toggle in your HN preferences.

> Another relevant factor is that the older technology used on the IBM keyboard's controller PCB requires more power to operate than newer keyboards.

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).

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.

The IBM draws around 112 mA from the interface, whilst a modern keyboard draws 1.2 mA. These figures are with the 3 status LEDs (NumLock, CapsLock, ScrollLock) off. Each of these draw around 12mA when lit on both keyboards.

That's a worst-case of 148mA, which even allowing for an extreme additional 100mA drawn by the converter is still well below the 500mA a USB port should be able to supply. I suspect the problem is actually signal integrity, and the fact that modifying the board to add stronger pullups works is more evidence in this direction.

Indeed, I'm not sure how they came to the conclusion that stronger pull-ups would reduce power draw. If anything they'd increase it.

And it won't affect MCU power draw at all as PS/2 is open collector - the MCU is never driving the data or clock high at all.

The author did not say that the resistors decreased the power consumption, or if they did, I missed it. The stronger current draw on the IBM isn’t exceeding the USB power limits but it is causing a voltage droop on the mobo’s shoddy regulators or PS/2 interface circuitry that is rectified by effectively reinforcing the pull-up circuitry to boost the signal integrity by adding a second pull-up in parallel with the existing.

I don't think voltage drop has anything to do with it.

The voltage was high enough to drive the MCU so it's more than enough for the 2V threshold voltage of both sides.

PS/2 is open collector so when idle the signals will settle at VCC regardless of the pull-up value

The "fractionally lower voltage high" can only have been very close to 5V.

Adding stronger pull-ups would have given faster rise times and stronger drive so either the rise time was too slow for the superio or the extra juice helped protect against noise.

The author mentioned current draw but it has nothing to do with it imo

While 500 mA is a maximum for USB 1.x/2.x without extensions, a device is supposed to request it from the host, the default limit is only 100 mA.

I have a PS/2 Unicomp and recently tried finding a compatible converter because of a bug with AMD hardware on Windows 10 that causes PS/2 input to be delayed by up to 30s between each key (even when entered in quick succession) if all cores are pegged at 100%.

The best converters don’t lock up but still hard reset “under duress” when typing away. (The only good converter I found was by Tripp Lite.)

PS/2 may not be hotpluggable, but USB certainly is. Not clear what would have prevented unplugging/replugging the USB side of your PS/2 to USB converter.

> 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).

Ah that's weird: years ago I bought two of these "cube" adapters and used them for years and never had any issue. But then I also switched to Topre switches (HHKB Pro JP keyboard).

Isn't one the selling point of these adapters anyway that it's USB, hence you can hotplug the keyboard should it lock up (which never happened to me but when you use one, it's USB plugged into the mobo, not PS2).

The Model M is nice, but I still maintain that the Model F that preceded it is the best keyboard ever made.

I couldn't agree any more vehemently than I am agreeing right now!

I used to think the Model M was great. And then I bought a reproduction Model F and now I'm convinced the Model M's belong in the dumpster. Okay, maybe not, but they're definitely inferior. The F has a lower actuation force, which is nice for people like me who mash on the keyboard like monkeys. It also feels 'smoother'. The inner assembly is individual barrels instead of a single plastic barrel sheet, so repairing individual keys is a lot easier. Also it's held together internally with clips instead of blobs of melted plastic rivets, making it possible to actually get inside to replace flippers or barrels without going through an entire ordeal of 'bolt modding'. It's just a much higher quality overall.

If anybody is interested in a brand new (reproduction) Model F, they're still being sold: https://www.modelfkeyboards.com/

The reproductions are nice because they have a semi-modern layout (compared to the original Model F's that are generally available on eBay) and fully programmable controller, so you can give it whatever layout you want. It can also be physically configured to resemble the HHKB if you're into that sort of thing.

the Model F repro is on my list of keyboards to buy, the price is a little rich however.

I don't know how much better buckling spring is compared to the mechanical keyboard switches..

but I find the ortholinear or column-staggered layouts of keys to be a big improvement over the asymmetric row-stagger of standard keyboard layouts.

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.

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.

Yeah, this is woefully out of date. There are several more-recent mods for the Model M.

Some accounts have all their posts go straight to [dead]. Not sure of the reasons, but I’m sure @dang would know. All you can do is vouch for it if it’s a good comment.

There is a secret shadowban list. People say that someone shadowbanned will have warnings from Dang in their history, but more often than not it isn't true. Also some people are shadowbanned upon account creation. I try to tell people when they are shadowbanned and vouch for their posts when they are substantive.

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.

I'd imagine it would be very difficult, and would require a relatively powerful MCU. Ben Eater's made a few videos discussing how PS/2[0] and USB keyboards[1] work. USB's a vastly more complicated protocol compared to PS/2.

[0] https://www.youtube.com/watch?v=7aXbh9VUB3U

[1] https://www.youtube.com/watch?v=wdgULBpRoXk

You only need a bare minimum host controller (USB 1.1) to accept a keyboard, and hardcode everything in the firmware to assume one. A suitable MCU is pretty cheap:

https://hackaday.com/2018/11/30/new-part-day-the-twenty-five...

Looks like someone already made (at least the source) for an adapter based around that MCU family available:

https://github.com/zhuhuijia0001/ch559-usb-host

As for relative lack of availability, I think that says more about how many people want to use an old keyboard with a new computer (semi-common) vs. a new keyboard with an old computer (rare).

From your link:

> The CH554 is a microcontroller with an E8051 core with a 24 MHz clock, a little more than 1 kB of RAM, and a bit more than 14 kB split between the code and data Flash.

I think that qualifies as "relatively powerful" when compared to a Z80 or 6502. :-)

I do agree that the lack of such adapters is due to zero market demand though.

> Update Jan-Feb 2005: A reader has reported success in using this USB to PS2 Adapter

This article is 16 years old?

That adapter certainly looks like it is.

IBM ps/2 is the best keyboards that ever existed. Built like tanks.

No flashy leds just a very good keyboard!

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