Re: very strange C64 fault

From: Pete Rittwage <>
Date: Tue, 18 Apr 2017 08:31:38 -0400
Message-ID: <>
>> On 2017-04-18, at 13:56, wrote:
>> From your description of a sprite "almost?" touching the bottom of the
>> screen... And the fact that it's always at the same position, so that
>> it's
>> really repeatable points to a logic error, not a timing error.
>> Maybe it's a stuck sprite collision bit, that once set is not reset and
>> keeps
>> the interrupt low?
> For one, good example.
>> You could write a simple test program for that.
> Or check with the scope what happens with e. g. _IRQ line when it freezes.
> Putting in a freezer car and checking if you get a repeatable freeze state
> when it happens may also help. Provided you have an AR or similar.

VIC-II can exhibit very strange failures. I have a stack of "partially
failed" chips. One I recall works fine with everything, except programs
that have sprites on the bottom border (like Paperboy). Any sprite moved
down there displays as trash.


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Received on 2017-04-18 13:00:43

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