Re: C64 buses when RESET is asserted

From: Gábor Lénárt <>
Date: Thu, 11 Apr 2013 08:52:46 +0200
Message-ID: <>
On Mon, Apr 08, 2013 at 04:31:02PM +0200, Gerrit Heitsch wrote:
> Even with RESET asserted, the VIC still displays a picture on the
> screen. It can only do that if it is activly reading from RAM (and
> ROM) to fetch the data to be displayed.
> If you want to be sure, you can tristate the CPU from the expansion
> port using the _DMA signal.

Isn't that similar to the scheme how CP/M cartridge works? The situation is
somewhat familiar: an external device (a Z80 CPU in our case) wants to
control the C64 bus, so it needs to disable the 6510. However it's
interesting to note that CP/M cartridges have problem (?) with certain C64
models, otherwise maybe it's worth to learn from the schematics of the CP/M
cartridge to control the bus externally maybe?

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Received on 2013-04-11 07:00:04

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