Re: Blurry picture

From: Gerrit Heitsch <>
Date: Sat, 19 Nov 2011 23:46:14 +0100
Message-ID: <>
On 11/19/2011 11:05 PM, Segher Boessenkool wrote:
>> Another way I have been thinking about is to rig up a +12V regulator
>> and use a 6569R5 in a board made for the 8565R2 and supply pin 13 with
>> +12V. Shouldn't be too hard, the voltage doubler circuit is still
>> there, just needs a 7812 plus some capacitors. If we still don't see
>> grey dots then, this suggests it's something with the 856x-VIC.
> Before doing such major surgery,

That's not really major surgery, it would be fully reversible and mean 
only one bent pin (13) on the 6569R5 and some open wiring. I have a demo 
that will produce the grey dots reliably.

> maybe we should get some more data first:
> get scope traces of all the relevant signals (clock, VIC #CS, R/#W, #AEC,
> #RAS, #CAS, some A and D pins) on various different machines. I couldn't
> find a single bus trace online.

I can see if I can get around to do some of those. Which signal in 
relation to what interests you most? I don't have a logic analyzer, just 
a digital scope though.

>> I could, but the C64C I have access to at the moment (the others are
>> stored away) doesn't show the vertical bars. Most C64C only show them
>> somewhat, they are really visible on a C128 though.
> None of my C64C do (and no dots either!)

There is a problem with using the term C64C. I own one that says that on 
the bottom, but still contains a 250466 board, that means 65xx-parts and 
82S100 PLA. It's better to use the board part numbers. The board with 
the large PLA is the 250469.


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Received on 2011-11-19 23:00:19

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