RE: [stella] Cartridge read timing problems?

Subject: RE: [stella] Cartridge read timing problems?
From: "Pension Maricel" <Maricel@xxxxxxxxxx>
Date: Tue, 20 Apr 1999 09:18:29 +0200
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-----Mensaje original-----
De: Mark De Smet <desmet@xxxxxxxxxxxx>
Para: stella@xxxxxxxxxxx <stella@xxxxxxxxxxx>
Fecha: martes 20 de abril de 1999 2:20
Asunto: [stella] Cartridge read timing problems?

>If many of you recall, I'm working on the great atari development
>system/game server.  Currently, mainly on the game server.
>I am having slight quirks, and maybe someone out there may know why.
>The hardware:
>Attached to the atari bus(the A+D line out of cartridge socket), is a
>screensaver ROM(it is just an atari rom that John Harvey wrote for me),
>and the output of a octal 3-state buffer.(I'm using a 74HCT541)  The
>address lines go both the the screensaver ROM, and into a MUX(3x 74HCT157.
>The output of the address mux's and the input of the 3state buffer go to a
>couple other roms(and later other stuff).  It is configured so that only
>the screensaver, or the buffer reacts to the atari's reads(atari A12).
>When setup for the screensaver, runs fine. when setup for the other
>roms(through the 3state buffer & MUX's), only 'mostly' runs.  In this
>state, the output of the 3 state is only enabled when the atari reads(and
>in this state), and the mux's select the atari address input to be passed
>on to the other roms.
>What happens:
>The ROMs are currently a pile of 'commerial' software.  The problem is
>that the games run improperly.  All games at least start up.  Some games
>seem to run, and crash later.  Others display wierd graphics.  For
>instance, Adventure, the power up screen looks like this:
>#x             x#
>#x             x#
>#               #
>#               #
>#       1       #
>#               #
>#               #
>#               #
>#               #
>#######   #######
>where the x's are a patch of boarder that appears and dissapears.  It
>flickers on and off irratically.  Boths sides flicker at exactly the same
>time, but it does not appear to be periodic.  The patch is exactly the
>same width as the edge(2 playfield blocks, I think).
>I believe the problem has to do with the 3 state buffer(the other rom's
>are 150ns, and should be plenty fast enough).  When changed to an ALS,
>games by and large behave better, but still crash and have funny graphics
>problems.  My best guess is that because the atari doesn't give the
>cartridge a real read signal, but instead just makes the cart(and hence my
>buffer) base it's output on the address, that my buffer happens to either
>hold the lines driven too long, or more likely not long enough.
>Any ideas about timing?
>Any ideas about what else may cause such software actions?
>Mark De Smet
>Archives (includes files) at
>Unsub & more at

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