2600 Cheats?

[Tsukasa]

Ze_ro, I thought that the gamegenie encryption was already cracked?

I know that there are programs out there that convert patches for the nes into gg codes. To make a similar device, all that you would have to do is note the differences between a bin file and the bin once it has been run through cheetah. Then you could burn the code to an eprom and use a multiplexer of some sort to insert the code from the eprom into some built-in sram on the cart. Then the game program could be read, and put onto the sram as well. Then the enable line could be activated and the atari could run the game as normal. The whole process could be performed by a microcontroller.

[Nukey Shay]

So you would need to burn a seperate eprom for every code you decided to use?? I like Albert's idea better (use a CC and load the game from a program on a seperate computer or PD...that program altering the bytes before it's fed into the CC).

[Tsukasa]

No, I mean store the code for cheetah on the eprom and plug the game cart into the device. The microcontroller and other on-board hardware would do everything that cheetah does only without a computer.

All you do is enter the codes just like if you were using cheetah, it would be just like an actual gamegenie.

[Robert M]

Many 2600 games have a bug in the player controls that can be exploited. You see the joystick has 4 switches which leads to 16 combinations. Only 9 of those 16 combinations are valid joystick positions. The other 7 positions are impossible for a normal joystick to ever produce. If the code uses a lookup table to translate joystick values to actions/movement then 7 bytes of the table are never used by the joystick. Space is at a premium in Atari ROMS, so often the 7 unused bytes in the joystick table are used for something else.

 

The result of all this is that illegal joystick positions can often be exploited to the player's advantage. I know that this works on Ms. Pac-Man and Venture for instance. Pressing Right and Left at the same time will move the player up to the right in Venture and allow the player to pass through walls! You have to experiment with games to see what happens with illegal joystick positions. Some games properly filter them out and so they have no effect. Other games desperate for space may yield useful results. If you open a joystick, you can press the buttons in any combination you want to see what happens in the game.

 

Cheers!

[Tsukasa]

Like how if you push left and right on combat at the same time you move faster?

[Nukey Shay]

The "better late than never" dept:

 

The Frogger cheat in question is $FC76 -> $2E (Cheetah code = C762E0). This redirects the DECrement lives command to point to the 2600's "dead" ram addresses instead of the #lives pointer for both players.

 

Here's a "boring" bin with the above change. I also changed the look of the turtles to keep a visual aide reminder that this cheat is active.

Boring_Frogger.zip