Re: cbm 8032 motherboard + 4164

From: Gerrit Heitsch <>
Date: Thu, 13 Oct 2016 16:34:07 +0200
Message-ID: <>
On 10/13/2016 09:30 AM, smf wrote:
> On 13/10/2016 07:21, Baltissen, GJPAA (Ruud) wrote:
>>> On a c64 that should also give you the advantage of being able to
>>> avoid the VSP memory corruption.
>> Please explain a bit more.
> VSP is a whole screen scrolling technique used on the C64, however it
> isn't stable. It depends on the demo, the C64 and the temperature.

I think it mostly depends on the combination of VIC and DRAM maker. If 
you have a C64 with a VSP problem, try different RAM (different maker, 
faster or slower)

> But if you're able to upgrade the C64 ram using static ram, then you may
> get it for free or at least you can build it into the circuit.

Since VIC only does read cycles you won't need a VSP fix. The problem 
with DRAM is that a read cycle is also a write cycle (writing the data 
back into the cells) so data corruption is possible. With an SRAM VIC 
might just read defective data, but won't corrupt it.

Also, replacing the DRAM in a C64 with SRAM is simple, you need a 128Kx8 
SRAM, a 74HCT573 and a 74LS32.


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Received on 2016-10-13 15:01:43

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