So, good news! I got the keyboard on Friday (3 days early, if I'm counting correctly).
The keyboard works fine, and looks good, and it's very nice to type on.
However, there are things that I didn't know that caught me out:
- First off, the 122-key 5250 Emulator keyboard has a different layout to the PC/122 5250 keyboard, which means that you might want to buy a set of PC/122 5250 keycaps if you buy the Emulator 5250.
- Secondly, the layout does not include a numlock key! It doesn't matter for me (and can be fixed with a custom keyboard layout, which I'll explain later), but it's good to note so others don't get caught out.
So, to solve the few issues (other than that, it's a great keyboard!), you need to replace the key caps, and also make a custom keyboard layout.
Now to get the keys, I had to boot into Linux (using a live CD / DVD), and run some tools!
I followed the advice in
https://wiki.archlinux.org/index.php/extra_keyboard_keys, which was using
showkeys --scancodes
in a Linux console (not one in a Terminal window! using the console that takes up the whole screen). This got the keys that Linux already recognized, which I noted down onto a sheet of paper.
I then used
dmesg
to show me what the scancodes were of the keys that Linux did not recognize, and so ignored except logging an error.
Now with all the positions and scancodes of the 122 keys, I rebooted into Windows to make a custom keyboard layout.
So to help me, I used a guide (
http://www.seasip.info/Misc/122key_nt.html) on getting the extra function keys on such a keyboard to work.
This guide was helpful, but it did not handle all the keys, so I had to do some further modification to the
kbd.incfile to make sure that all the keys matched what I wanted.
Another source of information that was helpful was
http://www.quadibloc.com/comp/scan.htm, as it contained information about scancodes, and helped me understand the printscreen and pause/break buttons.
Oh, by the way, it might be tricky to remap the "print screen" and "pause/break" keys once you find them (they are the keys that send the really long scancodes,
E1 1D 45 for pause/break, and
E1 2A E0 37 for Print Screen, as from what I can tell, Windows appears to do some special case handling for them.
Once I did all of this, I managed to get the whole thing working how I wanted it.

I'm happy to help anyone else who needs similar help, but I am currently too tired to it presentable.

(waking up at 4AM to throw up is not pleasant at all, and so I'm feeling so sleepy

)
It would be nice if there was a microcontroller based way to remap scancodes from a PS/2 keyboard to a PS/2 computer, but as I only plan to use this keyboard for this computer, It would be overkill, and a keyboard layout is much less risky to make.