Re: [stella] Four-player adapter?

Subject: Re: [stella] Four-player adapter?
From: Mark De Smet <desmet@xxxxxxxxxxxx>
Date: Tue, 15 Sep 1998 16:30:24 -0500 (CDT)
> >  Can you ask him if he's wired (any) Nintendo controller to an Atari, and,
> >if so, what chip he used?  I'm new to electronics but would like to try this.
> >
> I personally wired a Nintendo controller to a 2600.  The 7800 model is more
> difficult.  Anyway, I don't have the specs with me, but basically, you must
> remove the chip from the NES controller.  Be careful not to remove the
> traces.  Atari was based on an analog controller setup, so the digital chip
> is useless.  Once removed, you hook the Atari controller wires to certain
> pin holes and solder them into place.  No chips necessary.  I needed a few
> resistors for the 7800 NES joystick, but that was about it.I don't have my
> specs with me (they're at home)  but I'm sure I could get a hold of them.
> But that's basically the start.  

That is a method that works.(I know because John made his like mine)  
Essentially it is using the controller for the buttons.  Simple,
Effective.  When I made the original statement indicating that it was easy
to connect such controllers to the atari, I wasn't thinking of makeing
modifications to the controller.  I thought you were asking how you could
make an adaptor.

To get around the fact that the NES and SNES controllers have 8 and 12
buttons respectively and only 7 pins, the designers implimented them with
shift registers.  The nintendo controllers have pins for: Power and
ground, a clock, a 'load' in signal, and serial data out.  I dont know
what the other pins are intended for...

An adaptor can be devised using a shift register, buffers and a fast clock
to allow the NES controller(unmodified) to be plugged into the atari, and
be compatible with standard controllers.(Atari controllers are really
digital in nature, but don't actually contain digital chips).  This would
require probably only 3 small chips, and could be designed by anyone with
basic knowledge of digital logic.

An alternative exists depending on what your interest is.  You CAN simply
wire an (unmodified) NES controller into the atari without an adaptor,
BUT, you would have to write your own program.  You can use two of the
lines as outputs from the atari, and send the load signal out to load the
register, and send a clock signal out to readin the 8 bits of the shift
register in an input line.  Using a method based on this, with a
multiplexer and demultiplexer, you could probably have up to 32
controllers, and be able to read all 8 buttons(not just 5).  But I doubt
that you could program a game that can utilize all that information...

Mark De Smet



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