Re: Vic problem

From: Marko Mäkelä <>
Date: Fri, 25 Sep 2015 13:26:02 +0300
Message-ID: <20150925102602.GA1831@x220>
On Thu, Sep 24, 2015 at 05:34:53PM -0700, Terry Raymond wrote:
>but one keyboard the restore  key barely responds

This is normal, I think. On the C64 there is a heavy debouncing circuit 
on the RESTORE key, which has a dedicated line, not part of the keyboard 

>This NTSC Vic when powered up takes a little longer to display the Rom 

This is also normal. I suspect that it is holding the RESET line low 
longer than the C64 does. Because of this super-long delay, my Vic Flash 
Plugin firmware skips the RAM check, to get the start-up time somewhat 
at par with the C64.

>I will see how the Vic-20 acts this time so will mention the results.

On the Vic-20, the RESTORE key is not debounced at all. If you carefully 
half-press or shake it, it can generate enough NMIs so that the computer 
will hang or crash due to stack overflow. (Pressing RESTORE alone should 
have no visible effect; the NMI handler will check if STOP was pressed 
as well. But when you half-press, you can get the stack overflow.)


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Received on 2015-09-25 11:00:08

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