Re: C128 PLA dumped!

From: Marko Mäkelä (
Date: 1999-01-19 20:51:02

On Tue, 19 Jan 1999, Nicolas Welte wrote:

> Since I have no experience at all with techniques to reduce this truth
> table to a set of equations, I want to leave this task to others. Maybe
> there will be a little competition who solves this first.

First of all, thanks for doing this!  Soon there will be one secret less
about Commodore computers. 

I have the experience and tools, but I lack the time.  I reduced the
CHAROM equations from 245765 to 84 using a BDD-based tool (Binary Decision
Diagrams), but the equations could probably be reduced further.  BDDs are
sensitive to the order in which the variables are introduced in the

> The file is only available from my own server right now, but I'll upload
> it to funet as well.

It's now available from /pub/cbm/firmware/computers/c128/

> BTW, I can still be talked into providing a more complete dump, with 26
> inputs and 16 outputs.

This is not such a big task.  Now you have wired the 2 untied inputs to
fixed values, right?  Then produce 3 other dumps using the 3 other values 
(move the two inputs from their current setting to the other setting, one
at a time (e.g. 00->01->11->10), and you don't need to solder so much).
The dumps can then be catenated together.  I have access to a 512 MB
computer, so there shouldn't be no swapping problems when I generate the
equations from the dumps.

With rather simple rewiring, you could produce 4 dumps of the remaining 4
output bits as well.  My simple program is designed for byte-aligned truth
tables, so don't try to pack 2 samples to one byte. 

> And I'm not going to dump all 18 output bits, because the use of the
> extra two is pretty obvious. 

It may be, but I'd like to see them anyway.


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