Picture a device roughly the physical dimensions of a regular GBC cart, but thicker from front to back in some places. Especially when plugged into the GBA, the whole device could almost pass for a GBC game. Turns out that extra thickness in the back can accommodate a GBA cart. A small switch on the top of the unit enables or disables codes so you can play normally without cheats turned on. That's the 'all or nothing' feature. With the
Code Breaker GBA turned on, powering up your GBA shows the normal Nintendo logo and boot sequence followed by a notice that this device is in no way supported, endorsed, affiliated with, related by birth or ancestry, or standing within 50 feet of Nintendo. And then
Code Breaker GBA will try to autodetect the game cart you've inserted and choose a match among its pre-loaded codes. If it finds the game (and most all the big GBA releases are here) you then need to turn on cheats you want. WARNING: The part about not turning on conflicting cheats is not a joke. Doing so can crash your game, which just isn't a good thing. So, although it won't be immediately obvious which cheats conflict, use good judgment.
Once selected and flashing, a cheat is active. Multiple cheats can be activated, and then a quick stab at the Start button and you load the game as usual. But you will find that your chosen cheats are enabled, sometimes verified by a special screen that shows the game's Cheat Mode is open for business. Other times, you'll just see the results of your cheats as you play. Basically, if the game has a special 'cheat' screen, it will open up once the master code is enabled. So, what happens if you fire up a game with no code? I did, in the case of Rocket Power Dream Scheme. Browsing through the Pelican manual, you'll read how to edit codes and add them by hand. You need some kind of Internet access to get to the official Codebreaker Cheat Site which is the site that hosts updated codes and supports a wide range of cheat devices for multiple platforms. Once I got to this site, it was easy to browse through the the GBA section and find my game. Turns out there are 2 codes available, plus a master code. So, I added the code by hand, exactly as shown online and the next time I booted my GBA, it found Rocket Power in the list and I was ready to party. Don't take this one as an example of how many codes are available, since Castlevania had 190 separate codes last I checked! Everything you can imagine in a game plus a few things you can't image are available to be opened up by this little thing. You'll be wondering how you ever did without it, so long as you don't have some aversion to cheating.