geekhack

geekhack Projects => Making Stuff Together! => Topic started by: hjalfi on Wed, 01 February 2023, 16:25:24

Title: Reverse engineering an IBM System/40 typewriter keyboard
Post by: hjalfi on Wed, 01 February 2023, 16:25:24: 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:

[attach=1]

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.

[attach=2]

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.)
Title: Re: Reverse engineering an IBM System/40 typewriter keyboard
Post by: fpazos on Wed, 01 February 2023, 16:30:27: 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.
Title: Re: Reverse engineering an IBM System/40 typewriter keyboard
Post by: 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.
Title: Re: Reverse engineering an IBM System/40 typewriter keyboard
Post by: hjalfi on Thu, 02 February 2023, 15:17:41: 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.

Probably, but I don't really want to destroy a perfectly good piece of vintage (and slightly rare) hardware...
Title: Re: Reverse engineering an IBM System/40 typewriter keyboard
Post by: hjalfi on Sat, 25 February 2023, 15:22:57: 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.
Title: Re: Reverse engineering an IBM System/40 typewriter keyboard
Post by: fpazos on Sat, 25 February 2023, 15:38:48: Nice work!!! I'm glad you finished it