On Wed, 31 Oct 2001 ncoplin@orbeng.com wrote:
> Hi William,
>
> >Since it is intended to test ROM, RAM, and I/O, there is no point starting
> >in the Ultimax mode and then switching.
>
> Except to maybe an idiot like me, if it has a black screen before and after
> the cartridge gets inserted I am no wiser as to whether its something simple
> like the Kernal rom or a reset problem :)
Exactly. The KERNAL ROM routine executes one RTS instruction before
jumping to the cartridge code. If the RAM at the top of the stack area
(somewhere around $1f0-$1ff) is broken, executing the RTS may fail. As
there are numerous other reasons for the screen remaining black, the
starting method applied by the cartridge is not very useful.
Marko
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