Selecting the game

Top and Bottom PCB, low resolution, probably final version

The Atari Cosmos actually has all the games built into it, so a method is required of actually selecting which game to play. The solution is on the top left of the display board, shown here on the left, the five pads are contact pads for wiring on the "cartridge" - which is actually just the holographic dual image in some kind of box.

There are four potential Input lines IN0..IN3 remaining on. If you look at the PCB picture from the last post you will see the fifth from the left on top goes up to the display connector via a resistor - this is the far left connection on the display connector on the PCB track side. This is pin 19, IN0. I conclude this line is the game selector feedback and there are four outputs, each of which are interrogated in turn by raising an output line. If a signal comes back in IN0 that pad is connected, giving us a 4 bit binary number.

It is probable, no more, that this is the D line, because there are 4 D bits going to the display card and 3 bits on the G line, it's easier again on code space. It is possible that one line is 'on' when a cartridge is plugged in and the other three game select. In which case it might well be 3 G and one D line, who knows.

Of course, without either cartridges or a ROM dump there is no way of figuring out which game is which bit pattern, but we'll get round this with equates or something.