Wikipedia:Reference desk/Archives/Computing/2021 May 25

= May 25 =

USB keyboards thru PS2 and DIN adapters: one works, another doesn't
Hello, Thanks, 77.147.79.62 (talk) 09:16, 25 May 2021 (UTC)
 * What works: An old Windows PC (no USB or PS2) plugged with: keyboard DIN port - DIN-to-PS2 adapter - PS2-to-USB adapter - USB kbd what works (I-Rocks KR-6170-WH, added ~2007).
 * What doesn't: Another USB kbd intended as a spare (HP PR1101U). Works off the USB port of a recent computer, but not on the old PC!
 * Tests: USB kbd1 works. Hot-swap with kbd2: no dice. Plug back kbd1: works. Carefully plug kbd2 again: nothing doing. Windows shutdown, turn off then on again: kbd2 doesn't work at boot (no ESC for stopping checks, etc.) nor after Windows loads. (Win98SE with standard kbd driver.)
 * Question: I've been told it's because PS2-to-USB adapters are wired to only work with the kbd they came with, haw! Seems unlikely to find a generic adapter today. And I'd rather not tinker with some ISA card (upsetting a stable config with a mess of drivers). So I reckon I need to find either a PS2 or USB-slash-PS2 kbd. Are those indeed my main options at this point?


 * The PS/2-USB adapter is usually a dumb passthrough device. PS/2 port notes that the wiring for those adapters wasn't standardised. The chip in the keyboard has to have special support to detect that it's plugged into a PS/2 port, at which point it talks that protocol, rather than the USB HID protocol. It's not easy to determine which new keyboards still have PS/2 fallback support (and what adapter they'd expect); if it doesn't ship with an adapter, it's not safe to assume it still has the PS/2 fallback support at all. In your position, I'd probably go on eBay and either buy a PS/2 keyboard or one that explicitly says it has a PS/2 adapter. -- Finlay McWalter··–·Talk 13:12, 25 May 2021 (UTC)


 * Having looked at (UK) eBay, there's plenty of PS2 keyboards, including some that are very cheap. But, if you're buying online, make sure it's either a reconditioned/oldstock keyboard, or they actually show a PS/2 or DIN connector in the photo, as some online sellers just seem to put "usb/ps2/rs232" on keyboards that may be too new to really support that. -- Finlay McWalter··–·Talk 15:02, 25 May 2021 (UTC)


 * It sounds like you have a 5-pin DIN keyboard connector like on the old XT/AT IBMs. Those old Model M keyboards had the very best clicky action ever, if you like that sort of thing. You may find some help with your question here. It looks like most of the adapters you mention only contain wires to match up the signals (dumb passthrough as Finlay said above). It seems likely that you may need an active DIN-to-PS/2 device containing a micro-controller; these may still be available, such as discussed here. Some user projects such as this one contain software/drivers to run on the Teensy controller from Arduino. This may not be what you want, depends on your technical ability. This thread examines the reverse possibility of connecting an AT keyboard to a USB connector. Old versions of Windows, such as 3.1, NT, and 95/98 could take a very long time to find a new keyboard, as long as several minutes. I seem to remember that hot-plugging a PS/2 kb never worked. HTH MinorProphet (talk) 15:33, 25 May 2021 (UTC)


 * I'm not sure an active adapter really makes much practical sense for almost anyone, really (which is why they're mostly a few homebrew projects, not a mainstream project made in a factory). For people with modern computers who want that old style mechanical keyboard feel, there are a number of manufacturers who make modern keyboards with a full 104 key layout on a USB connection, including those with buckling spring mechanisms; Unicomp bought the IBM keyboard production tooling and make modern keyboards with it. The other way around, people (such as the OP) who have a DIN PC (which must date from the mid to late 1990s) are squarely in the retrocomputing bracket, and those folks will typically want an era-appropriate keyboard for their vintage PC - converting some modern USB keyboard wouldn't be in keeping. -- Finlay McWalter··–·Talk 16:30, 25 May 2021 (UTC)


 * Still got my original Compaq Portable with extra 256K RAM card + 10Mb Ethernet, not that it helps the OP... Dipswitches, used to be my bread and butter. MinorProphet (talk) 22:47, 25 May 2021 (UTC)
 * The USB HID protocol that USB keyboards use is totally different from that used with PS/2 and the even older AT ports. If I understand things correctly, most USB-to-PS/2 and PS/2-to-USB adapters are passive. They just shunt the wires, and depend on the keyboard's controller supporting both USB HID and PS/2 and detecting what it's connected to. So this can be hit-or-miss, which would explain your situation. It depends on the keyboard itself. Also, PS/2 and older keyboard ports were never designed to support hotplugging. While it's true that it often works, this is never guaranteed, and it can even damage the port hardware. Again, usually this doesn't happen, but if you want to avoid taking risks...
 * If you want to spend money, well, a keyboard with the DIN port should work. Or, depending on your needs, have you tried just running the Windows 98 system inside an emulator on a modern computer? Modern systems barely blink at this kind of stuff. --47.155.96.47 (talk) 18:57, 26 May 2021 (UTC)

OP sez: Okay, you confirmed what I need to do, and I learned the whys on top. Thanks all, 77.147.79.62 (talk) 13:35, 1 June 2021 (UTC)

--Guy Macon (talk) 15:41, 1 June 2021 (UTC)
 * Clickykeyboards carries a full line of active USB to XT/AT/PS2 converters: https://www.clickykeyboards.com/product-category/ps2-keyboard-to-usb-adapter-converters/
 * Unicomp is still making oringinal IBM model M keyboards (they bought the factory and tooling) with USB interfaces: https://www.pckeyboard.com/
 * Model F labs has a newly-designed buckling spring USB keyboard: https://www.modelfkeyboards.com/product/f77-model-f-keyboard/