View Full Version : Model M Keyboard to USB adapter

July 21st, 2014, 11:29 PM
I purchased a few Belkin SOHO 4 port KVMs with DVI + USB and want to keep using my old IBM PS/2 Model M keyboards.

What PS/2 to USB adapters do you guys recommend for the old Model M keyboards?

July 22nd, 2014, 08:00 AM

Look for the "Blue Cube" one. Unless you want to go custom or hunt for a Belkin.

July 22nd, 2014, 08:20 AM
This should answer your question. (http://www.clickykeyboards.com/index.cfm/fa/items.main/parentcat/11298/subcatid/0/id/124184)

July 22nd, 2014, 08:38 AM
Hehe... I just remembered clickykeyboards, found the link, and was coming back to edit my post only to see that Chuck beat me to it :)

July 22nd, 2014, 09:11 AM
For what it's worth, I've also used a Cherry keypad with a cheapo PS2/USB cable adapter hooked inline with the Model M as an adapter. It works as well, so the "blue cube" isn't the only device that can handle this.

Ole Juul
July 22nd, 2014, 03:58 PM
In my experience a ps2/usb passive adapter works in most cases. Two modern computers with model Ms have worked that way for a long time here. Until more recently when I got a new KVM which seems to be sensitive to model Ms. A new USB keyboard has mostly but not 100% fixed that, so I'm thinking that KVMs are not all equal in their keyboard handling abilities.

I posted a similar topic a few months back, and it seems that nobody had any problems to report nor that anybody had used the active adapter in the above link.

July 22nd, 2014, 06:20 PM
Don't some KVM's get power from the PS/2 keyboard port? I know the Model M draws more power then most USB keyboards so that could be an issue.

July 22nd, 2014, 08:36 PM
After Ole's post about using a passive adapter, I got curious. I grabbed a Model M (1370477) and a passive adapter. First try was to plug it into a fairly modern system running Xubuntu x64. No problem--the keyboard worked fine. Next step was to try it with a much earlier SS7 ASUS P5A, running XP and NetBSD. Nothing on either. So the usability of the passive adapter seems to depend on the BIOS/Chipset of your host. Early machines with USB, probably not so much.

July 22nd, 2014, 08:51 PM
Wonder where the cutoff is for "modern" machines and passive adapters.

July 22nd, 2014, 09:04 PM
What is a 'passive' adapter? I'm pretty sure all of those USB/PS2 adapters have an MCU acting as a set of HID end points.

July 22nd, 2014, 09:17 PM
What is a 'passive' adapter? I'm pretty sure all of those USB/PS2 adapters have an MCU acting as a set of HID end points.

Passive to me would be the original Microsoft Optical mice, they came with a USB to PS/2 adapter and the mouse sensed what it was connected to and worked accordingly. Active means the adapter is doing some logic conversions to make dumb PS/2 devices work on USB.

July 22nd, 2014, 09:35 PM
Well, I'm sure that the one I have is active, cheap though it may be (I think I paid less than $2, shipping included).

It has a USB male on one end and two mini-DIN females on the other and a plastic lump in the middle.

Obviously, they're not all equal. lsusb shows this:

Bus 006 Device 003: ID 13ba:0017 PCPlay PS/2 Keyboard+Mouse Adapter

July 27th, 2014, 04:57 AM
A passive adapter is just wires and a housing. It requires that the device connected to it (keyboard, mouse) can do ps/2 "protocol". Experience shows that many can't.

July 27th, 2014, 06:24 AM
I'm not sure about the existence of passive adapters.

In the case of mice and later keyboards that were designed for passive adapters, the mouse or keyboard knew how to speak both PS/2 and USB. So the adapter really is passive, and the device is smarter.

Except for the very late Model M style keyboards sold by Unicomp/pckeyboard.com, I don't know of any Model Ms that speak USB. So for a passive adapter to work, the motherboard chipset would have to know to speak USB or PS/2 over a USB port. Can anybody point out a chipset that actually lists this as a feature?


July 27th, 2014, 09:33 AM
Given what the cheap active adapters go for, it's kind of pointless to look at "passive" adapters, isn't it?

Of more concern to me is that the Model M draws a significant amount of current; does anyone know for certain if this is above the 100 ma. USB standard limit (with all 3 LEDs illuminated)? I know of no PS/2-to-USB converter that takes an external power supply, do you?