Hi Ruud,
Ruud Baltissen wrote:
>> - when the C64 hang up, I saw pop up lines on the screen once about every
>> second at random places. These lines have the hight of one character and
are
>> filled with graphical nonsence but plm. 80% is white.
>>
>> With one exception, I haven't even the slightest idea were to start the
>> research. The exception is removing the 6526 to see if the strange
behaviour
>> still happens. So any idea or comment is welcome.
>The visual errors seem to indicate that there is a bus problem with the
>VIC-II chip, i.e. the CPU doesn't shut down properly when the VIC-II takes
>over the bus, and then reads some crap. And with both chips driving the
>address bus, it is clear that the CPU crashes. I don't know if the '816 is
>able to tristate it's address lines like the 6510 does. How do you handle
the
>CPU shutdown?
I agree with Nicolas. I've seen such a bus contention in build the DMA
section of the circuit for my application. I eventually resolved it on the
C64, but still have the problem (strangely) when I plug the card into a
C128. Also strangely, I had less problems developing the card for a "B3"
circuit board than I did for the "A" boards, so timing is slightly
different.
Try poking the vic to blank the screen before the load... this will limit
bad-lines and may let you identify which part of the circuit is the problem.
- Nick
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