Re: [stella] Cartridge read timing problems?

Subject: Re: [stella] Cartridge read timing problems?
From: Mark De Smet <desmet@xxxxxxxxxxxx>
Date: Tue, 20 Apr 1999 12:06:04 -0500 (CDT)
> Have you tried eliminating the 3 state buffer altogehter? I am not
> quite clear on exactly what you are doing, but if you just want to
> selectivly enable each of the other ROMS you should just hook the
> address and data busses from the cart slot directly to all the roms
> then just enable the appropriate one onto the data bus using it's chip
> enable line. The 2600 seems to have pretty good bus drive capabilities
> since the Supercharger has 3 RAMS, 1 ROM, and the SC custom chip on
> the bus. If address bus drive becomes a problem you could just throw
> in an bus buffer IC that is always on to give the lines some extra
> drive power.

The isolation(the 3 state for the data; and the MUX's for the address) are
because the bus with all the roms on it can selectively be switched to be
connected to the atari or my main processor system(an Intel 80188).  This
is because there is also a bit of SRAM there that I wish my system to be
able to read/write, and I wish my system to be able to read the contents
of the ROM's.  The system has 2 basic states.  1, where the in-between bus
with all the ROM's is connected to the atari, and one of it's chips is
selected for the atari to run off of.  2, where the in-between bus is
connected to my main processor bus so it can read/write to it; while the
atari is running screensaver ROM(that is directly on the atari bus).
(Yes, the atari is power cycled whenever the states switch)

> > 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).


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