RE: [stella] Has anyone tried this before?

Subject: RE: [stella] Has anyone tried this before?
From: "Dan Boris" <dboris@xxxxxxxxxxx>
Date: Sat, 7 Feb 2004 10:20:23 -0500
The problem you describe where the RAM code occasionally goes out of
control when instering the cart is exactly what I would expect to
happen. When you insert the cart you never know exactly which signals
are going to make good contact first. Since the ROM in the cart could
get an unknown set of signals it could easily start throwing garbage
onto the data bus. One bad bit on the databus at the wrong time will be
enough to screw up the execution of the program in RAM.

There is another danger to removing and inserting a cart with the system
on, you risk damaging the cartridge. If a logic chip recieves +5 volts
or signals on it's inputs BEFORE it gets a good ground connection, it
will put excess stress on the chip and may damage it. Electronic devices
that are designed to be removed/inserted into a hot system (laptop
PCMCIA cards for example) are designed in such a way that they are sure
the ground make contact before any other pin, usually by making the
ground pin longer.


> -----Original Message-----
> From: owner-stella@xxxxxxxxxxx 
> [mailto:owner-stella@xxxxxxxxxxx] On Behalf Of Bad Panda Bear
> Sent: Saturday, February 07, 2004 2:13 AM
> To: stella@xxxxxxxxxxx
> Subject: [stella] Has anyone tried this before?
> After I saw Thomas' lxa_test program, I started thinking 
> about ways of playing with code executing in RAM. One idea I 
> had was to use a 2600 to dump the ROM of a catridge. The idea is:
> 1) Load a fully functioning display kernel into RAM.
> 2) Remove the super charger/catridge from the 2600.
> 3) Insert the cartridge you wish to dump
> 4) Have the RAM code dump the cartridge content. I was 
> thinking of doing this by sound (in a format similar to what 
> the super charger uses), or if that doesn't work trying to 
> dump the data over the joystick port over to a PC (or maybe 
> an atari 8 bit).
> To experiment with this, I created the attached program.  It 
> starts with a red screen (note PAL colors are different). 
> When select is pressed, it loads code in to RAM and the 
> screen changes to green to indicate that the RAM code has 
> control.  When select is pressed again it reads from a byte 
> in ROM and then sets the background color to that byte. I've 
> tried this and I've found that I can indeed remove the 
> supercharger from the 2600 and then get different colors from 
> different cartridges. This works 
> on all my consoles, including my 7800. BUT, sometimes when I insert a 
> cartridge or remove a cartridgein a slow or awkward way the 
> RAM code seems to loose control and the screen starts to 
> roll.  I think that 
>   somehow a reset interrupt is being generated, because one 
> time when I 
> inserted SCSIcide the screen jumped to the SCSIcide title screen.
> I think I'll continue with this expeirment with a bit, just 
> as an excuse to learn how to program sound on the 2600.  But 
> I was wondering if anyone else had tried this before, and 
> what were the results?  Also, if this does work out, does 
> anyone think this would be usefull?  I tend to think it isn't 
> very usefull because most ROMs are available on the internet anyway.
> Dusty Reichwein
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