PET 4032 video RAM size/mirrors

From: Andre Fachat (
Date: 1998-03-27 16:33:27


I am wondering, having found no hard facts for my petindex:

The 4032 machines (with the upgradable-to-8032 board? are there 
4032 without CRTC (I think they are mentioned but not confirmed,
although 4.0 ROMs might have been applied...)), or any 4032
in general, what video RAM size do they have? 1k or 2k?
Is this memory mirrored 2 times ($8000 and $8800, or even $8000 and 
$8400) or 4 times (if 1k, $8000, $8400, $8800 and $8c00).

What about the 8032? The reengineered schematics suggest it
being 2k, mirrored 2 times ($8000 and $8800). 

Another thing: the PET is supposed to be able to blank it's screen
with PIA1 CA2 (also used as IEEE EOI line). I assume that this only
works for non-CRTC machines, is this correct?
(should be $e811,52/60 if I remember correctly...)

Ruud, are you sure that in your PET 3008 schematics PIA1 CB1 as well
as VIA PB5 are connected to VIDON, which is controlled by PIA1 CA2?
I assume the two should be connected to TVV (vertical sync), right?

Anyway, your 8032 schematics schow that VIA PB5 is still connected
to TVV, but I remember that I had to patch a certain game
that worked on our 3032 but not on the 4032! And as far as I remember
I had to patch it for the offscreen-check (well, I could be mixing
this up for trying to port it to the C64, so I am really not
very sure about that anymore). Nevertheless the question is,
is VIA PB5 still the offscreen (or vertical sync) signal in the CRTC

Can anyone with a real machine confirm that please?


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Andre Fachat, Institute of physics, Technische Universität Chemnitz, FRG

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