Re: cbm 8032 motherboard + 4164

From: Marko Mäkelä <>
Date: Wed, 12 Oct 2016 08:34:11 +0300
Message-ID: <20161012053411.eim3q2dasa74dct4@x220>
Hi Ruud,

On Wed, Oct 12, 2016 at 05:15:44AM +0000, Baltissen, GJPAA (Ruud) wrote:
>Hallo Gerrit,
>> 41256 need 8Bit refresh...
>Nope. Otherwise the Finnish's and the 64'er's 256 KB hack on the C64 wouldn't
>have worked.

The VIC-II in the C64 (as well as the VIC-IIe in the C128) implements an 
8-bit refresh counter. That was proven in 1994 by the test program that 
Andreas Boose wrote, to check which memory addresses the VIC-II chip is 
reading. (On each line, for 5 clock cycles it would read from the 
$3f00..$3fff area. I cannot remember if the 8-bit counter was increasing 
or decreasing, for those 5 cycles per line.)

If there only is a 7-bit refresh counter available on the PET, Gerrit 
made a very valid point. Half of the DRAM could get corrupted, except if 
the program is accessing the 'missing' addresses frequently enough.  
But, unless I am mistaken, you would still get reliable 128 kilobits out 
of each 41256 chip.

Didier made a good point too. I would not want to have flying wires 
nowadays either. Back then I was young and brave (or stupid). :)


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Received on 2016-10-12 06:00:02

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