Re: VIC - DRAM-refresh

From: Ruud Baltissen (
Date: 2001-05-16 08:57:28

Hallo Bogax,

> but I'd sure look for /CAS-before-/RAS refresh capability,
> and I'd expect any 8MB FPM or EDO to have it.

I first must say that my question was initiated by Nick in a private email.
He asked if it is possible to connect 1 and 4 MB-modules to the C64 in such
a way that they could be used by the C64 _and_ the VIC. This automatically
means these modules have to be connected to/replace the original DRAM's. But
I decided that we lacked certain knowledge about the VIC.

Nick came up with the CAS-before-RAS (CBR) as well. The advantage of CBR is
that you don't have to worry about an own refresh counter. But then we still
must do it on a moment that the VIC performs the refresh for the onboard
RAM. Detecting BA as John suggested probably is not accurate enough. And
don't forget about the differences between PAL and NTSC.

For Nick:
The only solution I see for the moment is replacing the 4164's by 41256's
which enables you to use at least 256 KB of RAM accessible to the VIC.
Additionally you can add as much as other DRAM-modules as you want using
CBR. I can dream up a scheme doing that if you (or anybody else) want to.

Groetjes, Ruud

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