Compatibility
The e-Reader plugs into the cartridge slot of the Game Boy Advance like a regular game would. The end of the e-Reader sticks out from the Game Boy Advance unit to provide a slot to scan the e-Reader Cards. Electronically, the e-Reader is compatible with any console that supports Game Boy Advance games, however it may be mechanically incompatible with some systems (it simply does not fit), and the ability to link consoles may not be available.
Once installed, the link cable connector on the Game Boy Advance is obstructed, but a pass-through connection on the e-Reader allows link-up features to be used. The Game Boy Advance SP is also fully compatible, although the e-Reader doesn't mount flush with the SP (see picture). As the link cable connector on the SP is unobstructed, the pass-through on the e-Reader is not used.
The Game Boy Player is also fully compatible, and the e-Reader connects as it would to a Game Boy Advance (the e-Reader pass-through connector is used for connecting the link cable). The GameCube hosting this system acts as a Game Boy Advance - in order to link to a GameCube game, a second GameCube, running the game in question, must be used.
The e-Reader can connect to the DS Lite, but not the original DS. The e-Reader can however be modified to fit into the original DS, In either case, there is no support for linking features, as neither system has a link cable port.
The e-Reader does fit into the Game Boy Micro., and that system has a link cable port, however it is not a standard connector. A special Game Boy Micro Game Link Cable must be used for linking features. The Game Boy Micro's non-standard link cable port can not accept the Nintendo GameCube Game Boy Advance Cable, meaning it cannot link with GameCube games without modification to the cable.
Because the first version of the Japanese e-Reader did not have a link cable pass-through connector, it can fit into consoles which the later e-Readers are incompatible with. Even though Game Boys and DSs are region-free, Japanese e-Reader cards work only on Japanese e-Readers, etc.
Read more about this topic: Nintendo E-Reader