Stella 2.0 contains support for Bob Colbert's Cheetah cheat codes, as well as an extended Stella-specific type of cheat code that works on bankswitched ROMs.

To enter a cheat code, press Ctrl-C during emulation to bring up the Cheat dialog, and enter your code there. Press Enter when done, or Escape to abort if you change your mind.

Cheetah codes are explained in detail on Bob Colbert's web page, along with a list of codes for various games:

http://members.cox.net/rcolbert/

Briefly:

   6-digit (cheetah) code: aaaddc
   aaa = address - $f000
   dd = data
   c = count - 1

Cheetah codes don't support bankswitched ROMs, so they only work for 2K or 4K ROMs.

Stella's extended cheats are similar to Cheetah codes, except that they can be 7 or 8 digits long, with the extra digits used for the bank number:

   7-digit (stella) code: baaaddc
   b = bank (0 to $f)
   aaa = address - $f000
   dd = data
   c = count - 1

   8-digit (stella) code: bbaaaddc
   bb = bank (0 to $ff)
   aaa = address - $f000
   dd = data
   c = count - 1

Here are a few cheat codes I've found:

Pitfall (standard Cheetah codes):
   5b0ea1 - infinite lives
   723ea1 - infinite time
   aa5??0 - set starting level, ?? = 01 to ff (d0 is kinda neat)

Battlezone (Stella extended codes):
   1236ea1 - infinite lives

Ms Pac-Man (Stella extended codes):
   108fea1 - infinite lives

The next release of Stella (2.1 or 3.0) will contain a much nicer user interface for managing cheat codes, along with a database of cheats. If you've found any new cheats, please send them to me (atari@hardcoders.org), so I can include them in the database. Ideally, I'd like to collect at least infinite lives/time cheats for every game listed in stella.pro.

Enjoy!

--
B. Watson