Re: PCcard (2)

From: Marko Mäkelä (
Date: 2001-04-10 10:20:16

On Tue, 10 Apr 2001, Ruud Baltissen wrote:

> About compatibility: I don't know any valid reason why a good programmer
> would prefer the mirror addresses to program the VIC-II. So I presume all
> well written software should run on such an altered C=.

A programming error could cause the mirror areas to be written.  The
control registers for the internal RAM expansion in my C128 (sitting at
$d700-$d7ff) interferes with some C64 software, probably because they
are trying to write to color RAM ($d800-$dbff) but there is an index
overflow.  Therefore it is a good thing to have some way to disable the
control register.  In that expansion, I implemented it by connecting an
IRQ output of the 6821 PIA to one of its active-high CS inputs.  I don't
remember if I had to wire something extra to make sure that interrupts can
be triggered on the chip by software.


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