Re: Switchless ROMs

From: Marko Mäkelä <>
Date: Fri, 30 Dec 2016 12:33:37 +0200
Message-ID: <20161230103337.uxjmf4ncx7qszobo@hp>
On Thu, Dec 29, 2016 at 08:02:20PM +0000, smf wrote:
>On 29/12/2016 18:45, David Wood wrote:
>>Is it possible to detect a delay without a clock?  I suppose this is also
>>not infallible since accelerators could trigger it.
>It depends on whether the cpu could be stopped when fetching the 
>vector by dma (especially a vic bad line, but 8 sprites would do it 
>too). If it can then there is nothing to differentiate between a 
>delayed reset and the cpu just doing an lda $fffd lda $fffc from ram.

The CPU could also be stopped by a REU or something else that asserts 
-DMA on the cartridge port. That time is wildly variable. (For what it 
is worth, as far as I know, cartridges cannot access the KERNAL ROM. I 
would guess that any accelerator cartridge would have a copy of the 
KERNAL, or it would copy it to its onboard RAM using the 6510, not the 
CPU that is on the cartridge.)

Anyway, it is an academic question now that Jim decided to add an 
optional external reset signal for maximum compatibility.


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Received on 2016-12-30 11:00:02

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