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I've recently acquired an IBM 3151 Terminal without a keyboard and I'm not willing to spend any money on an original keyboard. This is why I've tried searching Google for any datasheets of the IBM RJ45 keyboard interface protocol, to no avail.

The connector is an RJ45 port.

Does anyone know what protocol those terminals used, so I can emulate the keyboard or possibly adapt a PS/2 keyboard? Are there any converters out there I just haven't found?

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    There's a whole lot more keys on a 3151 kb than a PC kb; You're going to have trouble just adapting a PS/2 kb. Besides, having the original kb is part of the experience.
    – RonJohn
    Commented Mar 15, 2021 at 1:35
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    Anyway... Here's the reference manual: bitsavers.org/pdf/ibm/3151/… It might help. (I found it by looking at the References section of en.wikipedia.org/wiki/IBM_3101 (which I found by googling "IBM 3151 Terminal").)
    – RonJohn
    Commented Mar 15, 2021 at 1:38
  • I have no direct knowledge of the 3151, but some other IBM terminals of that era (such as the 3179) use the same protocol as AT / PS/2 keyboards, with scancode set 3.
    – john_e
    Commented Mar 15, 2021 at 11:57
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    @RonJohn Thanks for the link. I agree, it would be nice to have an original keyboard, but unfortunately I don't have much money to spare, as I'm just some student interested in this kind of stuff. This is why I have to do this on a budget.
    – Unkn0wnCat
    Commented Mar 15, 2021 at 16:20

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I've recently acquired an IBM 3151 Terminal without keyboard and I'm not willing to spend any money on an original keyboard.

That's sad, as the keyboard is about the only reason to spend time with this terminal. That is maybe except for support of some wired IBM software, but that would most likely be also tailored to the keyboard as well, so better done with a PC emulation software anyway.

This is why I've tried searching Google for any datasheets of the IBM RJ45 keyboard interface protocol, to no avail.

The protocol is, to my knowledge, identical to PS/2, although with different scan codes. See this Table. IIRC Set 3 is what most terminals used. You may need some tryal and error to get the additional keys right.

The connector is an RJ45 port.

Pinout is

Pin Signal
0 NC
1 Ground
2 +5V
3 KBD Data
4 KBD Clock
5 Signal Ground
6 Ground
7 NC

Are there any converters out there I just haven't found?

Yes, there is Alexander Kurz' KbdBabel project. Haven't heared from him in a while, but the web page is still up, providing some information about protocols. While the Sourceforge repository has went into read only, it should be still possible to extract useful information.

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