Re: [stella] RAM carts?

Subject: Re: [stella] RAM carts?
From: Mark De Smet <de-smet@xxxxxxxxxxxxxxx>
Date: Tue, 22 Feb 2000 18:39:16 -0600 (CST)
> > The last(so far only) RAM cart I made(a long while back), was only a 4k
> > version, and had no PLD.  Further it supported the printer protocal.  By
> > this I mean that you could load it with the simple DOS command:
> > 
> > copy /b filename.bin lpt1 
> > 
> > (/b to force a binary copy, it will fail otherwise).  I had used the
> > strobe line to clock in the data and increment address counters. 
> 
> I remember reading about that after my friend and I designed the first
> version a couple years ago.. That was a pretty nifty way of approaching it.
> Our first version used custom software as well (though it was only DOS
> command-line based).  

It's main problem was that it was made with descrite DIPs.  Even still I
managed to fit it in two cart's glued end to end with battery and
all.(Note: wire wrapping is not too reliable :)

> With my current architecture this is not possible .. or at least I can't
> figure out how it would be.  There's bus contention on the 8 data bits
> because I wasn't able to 'abstract' (for lack of a better term) those
> through a CPLD - I ran out of pins.  Instead I high-Z the CPLD that drives
> the lines when the 2600 is playing.  This is something I really want to fix
> in the next spin, if there is one.

IC.  So, the atari must be off when programming then?  Can you get away
with leaving it plugged into the atari when programming, or do you have to
remove it?  I mean it wouldn't really do anything bad to the atari, but I
wonder if the voltages on the lines are enough to attempt to power up the
atari, or more likely that the current draw drowns out the CPLD.  I've
never tested this, so I was just wondering.

> The bankswitch chip is pretty near full.  It's a 72 macrocell version of the

That is useful to know.  One of the things I've been bothered with is how
big exactly it would be.

An interesting thought that I had was to use an fpga, and instead of
messing around with an eprom for it, to set it up so that it can be
programmed via the PC connection.  Just an idea.  First I have to make a
proto anyway.

Mark



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