[Coco] Sega Genesis Gamepad on CoCo

[J.P. Samson]

On Jul 6, 2009, at 9:21 AM, Andrew wrote:
> It would probably be best just to rip that chip out of an old  
> controller (I see them all the time at Goodwill) and re-wire it.

The chip is just a 4x 2-to-1 line multiplexer.  I figured if I just  
held the select high (pin one) by connecting it to the CoCo's 5V line,  
I'd be able to read the up-down-left-right-B-C buttons and map those  
to the CoCo using an Atari-to-CoCo adapter.

One day, I'll just have to slap together a breadboard and play around  
with the thing to figure out what is wrong with my thinking.

The later Genesis joypads were more complicated and had six buttons  
plus two left-and-right shoulders.  These were read by placing the  
joypad's IC in a special state by sending a carefully timed signal to  
it on the select line.  It was done in this way to ensure backwards  
compatibility with the old mapping scheme.

-- JP