# Re: Reverse engineering logic equations from truth tables

From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2002-06-25 10:47:42

```The following messages from André Fachat were rejected because of
unregistered sender address <a.fachat@gmx.de>.  I'm repeating them in
this single message.

On Mon, Jun 24, 2002 at 07:01:32PM +0930, Marko Mäkelä wrote:

> Nicolas Welte wrote: copying the plus/4 PLA?  And could someone

It is already there. I uploaded it together with a program to derive the
logic equations.

On Mon, Jun 24, 2002 at 12:13:29PM +0200, Gideon Zweijtzer wrote:

> If anyone is planning to do so, please note that generating a huge
> truth table for VHDL or verilog is a lot easier than trying to find
> the logic formula's yourself. Then run the VHDL or verilog to a
> compiler / fitter for a PLD and there you'll be able to find your
> equations.

Maybe someone with access to that can check whether my little program
http://www.funet.fi/pub/cbm/firmware/computers/pet/8296/82s100.tar.gz
has derived the right equations.

[My comment: there is a simpler way to verify the equations: create a
FOR loop x = 0 .. 2^n-1 and define the variables of your equation
e(v(0),...,v(n-1)) to be v(i) = (x & 2^i) != 0 for i = 0 .. n-1.  Write
the result of e(v(0),...,v(n-1)) for each x to a file, and compare the
result with the memory image.  (To be more precise, for the 82S100 PLA,
you'd write the results of all eight equations simultaneously as
different bits, and compare the result with the 64 kB binary image.)]

On Mon, Jun 24, 2002 at 09:56:05PM +0930, Marko Mäkelä wrote:

> Ullrich von Bassewitz wrote:

>> If I remember correctly, the technical manual for the CBM 6x0/7x0
>> contains the PLA equations.
>
> Where can the manual been found, and has anyone verified those
> equations against a PLA dump?
>
> Marko (who can see his CBM 720 again in 2 weeks)

I have used those equations in the VICE emulator. Dont remember whether
I checked with a ROM dump. Dont think so.

I dont know why, but currently I cannot find the manual on funet.
Have to look at my paper docs, maybe next weekend.

Andre

[My comment: wow, maybe André's tool could be used for simplifying the
C128 PLA equations.  It doesn't matter if it's an exponential algorithm:
we could let a bunch of computers to search for the minimal equations
for a couple of weeks.  Plus, I have access to a 128-processor SGI
Origin 2000 supercomputer. :-)  Just kidding, it's better suited for
memory-hungry problems.]

Marko

Message was sent through the cbm-hackers mailing list
```

Archive generated by hypermail 2.1.4.