RE: Commodore PLA equations (complete)

From: Bil Herd <*bherd_at_mercury-cg.com*> Date: Wed, 6 Jun 2012 00:12:47 -0400 Message-ID: <c0ef50f8a08c024f90eebc399f0e6ab1@mail.gmail.com> · bherd_at_mercury-cg.com

Once we copied the 82S100 to our own NMOS version the ultimate programing
of the array was done by the insertion of "diffusion slugs" and "pre-ohmic
contacts", layers 2 and 5 if I remember correctly.  When we made a batch
we would sometimes have half of the run held after making just the first
three layers, (held at 1-2-3) which set the number of OR terms if I
remember, however we could make some emergency changes just by changing
the mask for layer 5 .  Layer 7 was the passivation which we sucked at for
quite a while. I remember I had a couple of extra OR rows inserted that
were kind of meaningless but available for emergency changes.

The worksheet we used originally was straight out of the signetics
datebook.  For the 128 we outgrew the worksheet and made a text file,
which was hand administered.  We then gave it to the chip layout group
(usually called Calma after their CAD system) and they hand entered it.

-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Thomas Giesel
Sent: Tuesday, June 05, 2012 3:20 PM
To: cbm-hackers@musoftware.de
Subject: Re: Commodore PLA equations (complete)

> btw, at the end, isnt it all NANDs ? or NORs ?

How exactly it's done in the 82S100 is written in its datasheet: It has
(up to) 48 product terms which are AND combinations of any of the inputs
and inverted inputs.

Any of these 48 product terms can be combined to 8 sums, which are OR
combinations of the product terms.

The final result can be inverted (which is done with the CASRAM output
obviously, which re-uses most of the terms of the other outputs).

For my PLA clone (which should arrive in the next few days from
Donald...) I wrote the terms in exactly this form. Which makes no
difference as the CPLD synthesizer/fitter optimizes it anyway, even if it
is written in other forms - but it feels more original ;)

Skoe

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