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Reverse engineering an IBM System/40 typewriter keyboard

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hjalfi:
I have this fantastic 1985 IBM 6770 System/40 Quietwriter. The keyboard is a proto-model-M with an actual screen on it. I would like to build a converter to use it as a modern keyboard (with proper screen support, of course!).

(I did this massive teardown and demo here: )

Poking at the keyboard protocol with a logic analyser, it's... weird. I was expecting something like bidirectional AT, but it's not. All the data is expressed on a single wire (plus a reset line). It looks like the base station sends a high-frequency signal which either triggers the keyboard into reporting its state or announces to the keyboard that the base station is about to send. There's a constant stream of short packets, which suggests the protocol is polled. Here's a sample trace of one such packet:



Just to make life even worse... none of the chips on the keyboard PCB are identifiable! I wonder if IBM has anonymised them? The fact that two chips have consecutive numbers despite being from different manufacturers suggests this.



Before I start writing trying to figure out how this works from base principles, which I'm honestly not really looking forward to... does this look at all familiar to anyone?

(BTW: there's some more details on a superuser.com question here. https://electronics.stackexchange.com/questions/651458/what-is-this-single-wire-bidirectional-communications-protocol They weren't able to help.)

fpazos:
Sorry but the only thing I understand here is Mexico, I hope you find someone that can help you. People in reddit /cyberdeck sometimes use old technology for projects.

Lanrefni:
Probably be easier to map out the matrix on the keyboard and make a new controller for it,not sure about getting the LCD working though.

hjalfi:

--- Quote from: Lanrefni on Thu, 02 February 2023, 14:23:30 ---Probably be easier to map out the matrix on the keyboard and make a new controller for it,not sure about getting the LCD working though.

--- End quote ---

Probably, but I don't really want to destroy a perfectly good piece of vintage (and slightly rare) hardware...

hjalfi:
For completeness: I got this working, and can now use the keyboard (including the LCD attached to it) via USB! And it's completely non-destructive, too.

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