Re: Commodore 64 Ultimate Cartridge project

From: Gábor Lénárt <>
Date: Tue, 8 May 2012 17:37:19 +0200
Message-ID: <>
On Tue, May 08, 2012 at 05:23:10PM +0200, Gerrit Heitsch wrote:
> On 05/08/2012 12:12 AM, Gábor Lénárt wrote:
> >
> >The other complicated solution would be disabling 6510 and allow uC to place
> >data into C64's memory, so basically do some kind of DMA (from the view
> >point of the C64 - I mean).  Then I can have more tight timing, not needed
> >to think about slower transfer by 6510 program, etc.
> If you do this, you will either have to disable the display or take
> the bad lines into account. The latter meaning you have to watch AEC
> to see whether you can have the bus or not.

Yes, I found an old newsgroup thread about this, basically with the example
of the Z80 based CP/M cartridge where the topic is the same: disabling the
6510 and "drive the bus" from externally (by the Z80 in that case). However
it also made me think about one issue: as far as I remember there were some
user feedback that CP/M cartridge had troubles on some C64 models, though I don't
remember which ones and why. 

Btw, how much "used" the bus in C64 during normal conditions? I mean, is there
any time left when neither 6510 and nor VIC-II uses it, so it's possible
to use (slower) DMA with "running" CPU too. Sometimes that mode can be
useful too, if speed is not the main issue. I guess it's not so much a
realstic idea, as VIC-II even needs to steal cycles from the CPU from time
to time (badlines, and I am not sure about sprites, but maybe then it needs
extra cycles too). I am just curious here, I wouldn't do this anyway.

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Received on 2012-05-08 16:00:32

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