From: Gideon Zweijtzer (gideonz_at_dds.nl)
Date: 2003-07-06 19:18:50
Spiro,
> Mario wrote that there are colored squares *instead of*
> sprites when inserting a cartridge, so I assume that there
> are indeed sprites, but they have a wrong content. That was
> the reason for my advice.
My appologies, I missed that part of his message.
It is difficult to say anything when it comes to using a cartridge,
because the code used in the cartridge is usually not known. I read
Mario's second messgage, and it seems that the wrong data is being read
by the VIC-II. The colors are okay, so wrong writes to the VIC-II are
not likely, as the border color or other colors are likely to be
overwritten.
This could indeed be the CIA#2 for the A14/A15 lines, but I have also
had a C-64 before where logic IC's were broken (the ones that you'd
never expect to get flaky!). The A14/A15 lines go through multiplexing
logic before it arrives at the VIC-II. I think that with an oscilloscope
the bad guy can be found easily. Antoher method is, when you can still
type (blindly) is to type a small program to copy the character ROM to
RAM, and switch the VIC-II to retrieve the characters from there. (The
addresspath from the VIC-II to the ROM is different from the path used
by the CPU to the ROM!). You could try this in different banks. With
some logic reasoning, you'll find out where it goes wrong. This is how I
found out once that the 74LS373 latch was broken.
Gideon
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