Re: Additional SIDs

From: Segher Boessenkool <>
Date: Thu, 1 Dec 2011 23:40:36 +0100
Message-Id: <>
> Strikes me $D7xx is the best place for an internal SID  
> modification, being as that is spare in the C128 and actually  
> decoded. No idea who decided $D420 was a good idea, that takes way  
> more in the way of address decoding.

On a C64, there is no spare chip select you can use (you cannot use #IO1
or #IO2, de00 resp. df00, since cartridges already use those).  So you
split #SID into two using one of the address pins.  A8 is traditional
(putting the second SID at d500), A5 (d420) of course also works fine.
A8 makes the second SID available at d700 as well, nice for C128


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Received on 2011-12-01 23:00:18

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