Emulators of Classic Computers

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jan 15 16:41:32 2004

>
>
> >If it uses standard chips (i.e. data sheets exist), then it can be
> >reverse-engineered!
>
>
> Not if the uCode proms have rotted.

If the microocode PROMs are standard chips, then you can produce a
schematic without needing to know their contents. You can just take the
PROMs as a memory array taking in <m> address liens (from the sequencer)
and giving out <n> data lines (to the ALU control inputs, other logic,
etc). That's all the original schematic would have included IMHO.

I've never seen a schematic for a microcoded system that included the
contents of the PROMs. That information was provided as a separate
listing (if at all). Of course if you want to copy or emulate the device
then you need both the schematic _and_ the contents of the PROMs.

In any case, you should have dumped the PROMs already :-). As I keep on
saying, the time to start thinking about repairing a device is when it's
working. That's when you dump programmable parts, when you measure
voltages (like my comments on the H89 the other day -- you want to know
the CRT voltages when it's working correctly, so you can see which one
has changed when it malfunctions), when you record waveforms, etc. It's
too late to do this when the device has failed.

-tony
Received on Thu Jan 15 2004 - 16:41:32 GMT