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MM5740 Keyboard Encoder

CommodoreZ

Experienced Member
Joined
May 18, 2007
Messages
145
Location
Z Labs.
I've been studying the terminal logic board from a Heathkit H19 terminal, and the MM5740 Keyboard Encoder that it uses to convert the keyboard matrix into usable signals. However, I understand that the Apple I and II used this same encoder, and I wouldn't be surprised if more machines also used it.

I'm curious if someone has emulated the outputs of this device to allow for different kinds of keyboards to be used. The idea of turning say, PS/2 keyboard signal like-signals I'm sure has crossed somebody's mind before. Am I completely off my rocker here?
 

Christoffer

Experienced Member
Joined
Oct 15, 2014
Messages
299
Location
Denmark
Took a quick look, and it seems it outputs 7bit ascii + strobe+parity+repeat, so that should be very very easy to emulate. 7 on/off switches and a pushbutton could emulate its outputs, really.
If you took a computerized approach, it'd probably take an hour tops to get an arduino to do just that - it has a PS/2 library.
Even without, having a clock and a shift register could likely do the trick - plus a bit of logic.

A load of different keyboard encoders uses the "matrix in-ascii out" approach, they'd all be compatible, i'd think. Maybe not with the parity/repeated key functionality.

Interesting project, nevertheless!

--Christoffer
 

CommodoreZ

Experienced Member
Joined
May 18, 2007
Messages
145
Location
Z Labs.
I looked into things on the Apple side of the fence (where I don't normally venture) and it turns out many folks have come up with something comparable. I should have guessed, considering all the cool things people have added into their Apple II's Here are the examples I found to be the most descriptive.

Mike Willegal's approach & Sebastian Kienzl's approach

I'm sure these will get me started for the moment. However, any additional references are appreciated.
 
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