Keyboard Converting Guide
This is a preview of upcoming Admiral Shark's Keyboards content. This page is considered work-in-progress and should be treated as such.
The Keyboard Converting Guide is designed to help produce a tailored keyboard adapting or converting guide based on your answers to a series of questions asked to identify the keyboard and its connectivity. Please answer each question below with the answers that best apply to your keyboard.
Contents
- Connector: 6-pin Mini-DIN
- Protocol: IBM PC Mode 2 (Enhanced variant)
- Scancodes: IBM scancode set 2 (default)
The combination of a 6-pin Mini-DIN plug, IBM PC Mode 2 protocol and IBM scancode set 2 (but the ability to change sets) was used as the IBM Personal Computer Enhanced Keyboard interface. It is commonly known as the PS/2 keyboard interface, named after the IBM Personal System/2 family that popularised it. PS/2 is backwards-compatible with the AT keyboard interface. As the same physical plug is used for most mice of the same era, PS/2 plugs and sockets may be colour-coded purple for keyboards and green for mice.
The use of IBM PC Mode 2 protocol means this interface is related to the Display Station (terminal) and the aforementioned AT keyboard interfaces, which all share the same carrier serial format but differ in exact scancode and command set usage. An Enhanced variant keyboard is natively compatible with an AT host, and an AT variant keyboard can operate with effectively all PS/2 hosts so long as no software requires a scancode set change. A Display Station variant keyboard can operate on a PS/2 host provided the operating system and its keyboard driver supports IBM scancode set 3. An Enhanced variant keyboard can be told to switch to set 3, which theoretically makes them compatible with Display Station hosts. But in practice, it is unclear how much this was utilised (if at all) but IBM terminals.
Applicable keyboards
The following IBM and family keyboards are known to use this keyboard interface:
IBM Personal System/2 Enhanced Keyboard
IBM Personal System/2 Space Saving Keyboard
IBM Personal System/2 Host Connected Keyboard
IBM Selectric Touch Keyboard
IBM Space Saver Keyboard
Converting to USB
PS/2 to USB generally requires active conversion. Some PS/2 keyboards made since the advent of USB may offer passive PS/2 to USB support, but without documentation for a given keyboard, this capability should not be assumed. If it was possible though, a given keyboard's original box and packaging would likely indicate as such and would likely come with a bundled passive PS/2 to USB adapter inside as well (the latter applies for brand-new keyboards, not open-box or used keyboards where someone else may have included a non-compatible adapter accidentally or unwittingly). Thus, it is prudent to assume you will need an active PS/2 to USB converter in the absence of any information on the contrary.
Active PS/2 to USB converters are commercially available and generally affordable. They typically have both keyboard and mouse sockets present, but the latter can be left unused. The following are known active PS/2 to USB converter choices.
The common Soarer's Converter or Vial-QMK ibmpc_usb firmware both support PS/2 keyboards and can be used for a more costly but feature-rich converter. Notably, they both offer hardware-side layer, macro or remap creation. Both will advertise XT and AT support concurrently - that is normal. The following are currently available pre-made converters that are flashed with either firmware:
Note
If you already own an active XT/AT to USB converter running Soarer's Converter to Vial-QMK ibmpc_usb firmware, you can reuse the converter for a PS/2 keyboard if you combine it with a passive PS/2 to AT adapter.
If you can confirm your keyboard supports passive adaption, this would be the most affordable option. Such adapters are electrically simple and often generic, so there is no specific brand people may try to target. So long as the adapter looks like what is pictured above (note the number, placement and direction of the pins) and is labelled like "PS/2 to USB", "Mini-DIN to USB", etc. it should suffice. You should be able to find such adapters on eBay, AliExpress, etc.
PS/2 to AT needs only passive adaption. PS/2 keyboards typically work on AT hosts without fuss since their protocol is very similar and AT is limited to the same scancode set that PS/2 uses by default. Such adapters are electrically simple and often generic, so there is no specific brand people may try to target. So long as the adapter looks like what is pictured above (note the number, placement and direction of the pins) and is labelled like "PS/2 to AT", "Mini-DIN to DIN", etc. it should suffice. You should be able to find such adapters on eBay, AliExpress, etc.
Converting to XT
PS/2 to XT almost always requires active conversion. Whilst some third-party XT and AT compatible keyboards may have a switch to change between either compatibility, PS/2 keyboards (despite being very similar to AT) rarely ever received such a switch. Active converter solutions for PS/2 to XT indeed exist, but options are limited and prices for such may reflect that. The following three options work.