UNTESTED
Always wanted one of these for the original system, but they're hard to get so I've tried to recreate the cartridge itself for others to enjoy as well. For beginners and those with short memory, CP/M was professional choice of operating system for home computer markets - so if you wanted tax software, word processing and similar exciting tools this was the one you wanted for christmas. The system ran mainly on Z80-based systems while the Commodore 64 had a 6510 in it, so the cartridge was created in order to allow you to use the Z80 processor instead. Note that this is not a secondary processor, the Z80 shares all the main busses with the 6510 so only one of them can be active at a time.
There was no official schematic released for the module, none that I've seen anyway. Ruud Baltissen has taken upon himself the task of documenting the details of the module with a schematic, see his page at http://www.baltissen.org/newhtm/c64_cpm.htm for a lot more information on how the module works. My schematic has been transcribed from the one he made, then a PCB layout was done. Edge connector footprint was borrowed from the Open16KCartridge made by SukkoPera.