RE: 85xx <------> 65xx Mutually replaceable?

From: Gideon Zweijtzer (
Date: 2003-07-06 18:40:44

Spiro wrote:

> In fact, I really doubt a breaking charrom would influence 
> the displaying of sprites without affecting the 6510 in any 
> way - the only way I see the charrom could influence the 
> sprites is in that it "shortens" some data or address bus 
> pins, but in this case, even the 6510 would not be able to 
> see anything useful.
> What I see as possible candidates (the list is not complete, 
> there might be other things, too):
> - the VIC-II itself
> - the PLA
> - the CIA#2 (which generates the address bus lines A14 and 
> A15 for the VIC).

I think the CIA#2 is not a candidate, because changing the address lines
A14 and A15 to the VIC-II does not cause sprites to appear, as they are
being turned off in the startup routine of the C-64. It is more likely
that some writes to memory also reflect in writing registers of the
VIC-II, and hence I think it is the PLA.


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