> What really caught my interest is why there are no markings on the chip.
> It seems very strange. The operation is so simple there wouldn't be any
> reason to try to obscure the part number.

You may find that there is a number on the bottom of the chip if you remove=
 it.

I remember repairing an HP Plotter where the chips were all marked with HP =
part numbers. Another member of staff had isolated the faulty chip by swapp=
ing chips with a known good unit, then tried to get a replacement chip from=
 HP. They would only deal with the complete plotter at an exorbitant cost, =
so the plotter was put on a shelf. Then came time for a clear out and they =
were going to bin it, so I suggested my desk was a suitable bin, which duly=
 became the case.

On investigating the faulty chip I found it had '6802' printed on the botto=
m of it. Knowing that we had some other gear using Motorola 6802 microproce=
ssors, I dug out a chip and tried it - voila working plotter.



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