[sdiy] ETI447

[Colin Hinz]

On Thu, 8 Jul 2004, Paul Perry wrote:

> At 07:46 PM 7/07/04 +1000, Ken Stone wrote:
> >>I have some questions about this circuit. I think that the use of IC9, a
> >>4049 CMOS, are quite smart, but why are pin 16 connected to zero reference
> >>voltage?
> >because the chip is not being used as a digital chip. It is being used as a
> >row of FETs. (a case of using it in a way it was not designed to be used)
> >
> And not only that, some ETI synth stuff from the same time, would only
> work if you used the SAME CHIP MAKER as they did.
> Which is what can happen, if you are usign stuff out of data sheet range ;D
>
> Enven 'simple' things like input protection schemes can make a fatal
> difference.

Absolutely. I remember seeing an ETI parts list which specified specific
manufacturers and IC suffixes. Can't remember the project, though :=)

And does anyone remember the original Apple II motherboard, with its
amazing hodge-podge of logic families, carefully chosen to keep the
signal timing under control? It sure did work, though -- even the
"clone board" that I hand-assembled from scratch, using ICs I'd
scrounged from hither and yon, gave the friendly beep the first time
I powered it up. (And a darned good thing it did, too, as all I had
for debugging digital logic was a logic probe.)

- Colin Hinz
  Toronto, Canada

PS: in industry, a "bill of materials" will indicate specific devices
(manufacturers as well as complete part numers down to the "tape and
reel" specs) ALL THE TIME -- neither the purchasing people nor the
production people are expected to be able to make sensible
substitution decisions. That's where component engineering comes
in -- a thankless job if there ever was one.