Re: [stella] Cartridge read timing problems?

Subject: Re: [stella] Cartridge read timing problems?
From: Mark De Smet <desmet@xxxxxxxxxxxx>
Date: Tue, 20 Apr 1999 17:17:52 -0500 (CDT)
> >> > Any ideas about what else may cause such software actions?
> >
> >The thing that really puzzles me is that the games, do mostly run.  I mean
> >if my interface didn't meet the timing constraints, I would think that
> >there would be many more problems than just graphics issues(like the
> >program not starting up).
> Hmm.  You say that it seems like the ROMs all work fine, but there's
> messed-up stuff in the displays.  Could it be that your interface isn't
> quite decoding correctly, and is throwing stuff on the bus when the cart
> is not selected and the TIA registers are selected?  So it's interfering
> with TIA reads and writes, but the ROMs are okay?

The roms when wired directly to the atari bus work properly.  My hardware
has no decoding.  The address must be getting through from the atari to
the roms because otherwise, the programs wouldn't run at all.  there is
only a 3 state buffer between the atari and the roms, and that is enabled
whenever the atari's A12(the cart chip select) is high. 

Ya, the best possibility that John and I could come up with was that my
rom/buffer was driving the bus when a write is suposed to be going on
elsewhere on the bus.  The problem with this is that the buffer(HCT/ALS)  
is way faster than the old ttl logic that the games ran on.  If anything,
I would think that my buffer would shut off early.  However, looking at
the read/write bus cycles in the stella manual, the 6507 should be
aserting the address(and hence the cart chip select) for as long as it
wants the data, and I can't imagine my buffer being to slow in undriving
the bus.



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