Re: 'Frankenstein' Disk Drives, Done Cheap

From: Gerrit Heitsch <>
Date: Fri, 25 Apr 2014 16:24:26 +0200
Message-ID: <>
On 04/24/2014 10:51 PM, Groepaz wrote:
> On Thursday 24 April 2014, you wrote:
>> On 04/24/2014 02:06 PM, David Wood wrote:
>>> seems to be the
>>> trick.  I was linked this via IRC.  It doesn't actively search for the
>>> party, but instead latches the DRAM address before the VicII has a
>>> chance to change its mind.
>> I see what it does... If I understand it right that trick will only work
>> since _CAS on the C64 has to go through the PLA. If _CAS were directly
>> connected to the DRAMs, it would fail since the additional delay of the
>> 74xx86 and the 74xx573 would cause the DRAMs to miss their column address.
>> Did someone figure out what exactly happens inside VIC when this problem
>> surfaces?
> according to jens schönfeld its a setup-and-hold timing violation.

Yes, but why? The CPU was done with its part of the cycle a few hundred 
nanoseconds before this problem happens. What can the CPU do to VIC 
there that will only surface that much later?

I would expect that no matter what the CPU does, everything inside VIC 
had stabilized by then.


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Received on 2014-04-25 15:01:05

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