IC-99 Mystery (modification)

[Geoff Harrison]

Looking at those pictures of Erik's, it seems that machine has had several mods made at some time in its history, all of them were backed out except the one involving IC99. Someone has cut (and restored) traces and connected wires to IC pins that involve states that seek instructions and update the P register, plus some others that involve the K (data lamp) register. It's all quite tantalizing.

Fortunately, unless there are some other cut traces that I missed, all those mods have been restored.

[Cappellanus]

That modification on Eric Klein's machine is interesting because it is the first (and only?) modification known on a Kenbak-1. Common sense suggests that this should be an input or output, the only thing that a Kenbak-1 lacks to do "real work." We've probably all wondered how to make an input or output (of course, Grant's investigations show the light lines can be used, maybe with a low-pass filter.)

I seem to recall that Herbert Eisengruber (Nova Scotia) had some type of machine interfaced up to a Kenbak-1, but maybe I just dreamed this up. At one VCF meeting, in the pictures, I thought he had some later hardware that was hooked up to a kenbak-1, but now I can't find a source, and the pictures don't make that clear.

Look at this picture....
http://home.comcast.net/~msmith6020/P7160223a_copy.jpg
towards the bottom right of the picture is a photo showing a kenbak-1 with a later box on top of it. Was this a input/output interface? If anyone knows Herbert, maybe they could ask him. Herbert's machines came right out of a technical school, so I wouldn't expect them to have the modifications such as a privately owned machine could have attained.

In any case, maybe we'll never know details of why Erik's machine was modified, as a whole-big circuit board with lots of logic could have been interfaced into those few signals, and all that is long lost.

Oh, and Grant: I didn't get to the bank before they closed, so no money order. I'll definitely get it mailed by Saturday, priority mail. Don't give my kit away to anyone else!!!

[Architect]

Perhaps Eric's machine is the one that was modified by John's son. See:

http://www.bitsavers.org/pdf/kenbak/...baker_1986.pdf

At page 8 (last page) he refers to three machines: the prototype, the one that is now in the Computer History Museum and one modified by his son.

Just speculating.