A 6309 CPU can be used in place of any 6800 series CPU. Really, take a 6800 CPU off the board and put a 6309 there and turn the machine on, any machine. The only incompatibility to be concerned with is if the software relies on known errors/deficiencies in the 6800 series of CPUs (there is no logical reason for such usage except perhaps DRM, thus no logical reason). A surprising number of classic computer hobbyists replaced their 6809 CPUs with 6309s for what was thought to be minor gains (heat, stability) when the chip was first offered in 1982. But in April 1988, Hirotsugu Kakugawa wrote a "MEMO" (and open memo to the world) detailing previously unknown features of the 6309. It was not just a mere 6809 clone but an entirely more advanced CPU that ran in 6809 emulation mode by default. It would in fact replace any 6800 series CPU and automatically emulate them as well. But, even when it was in emulation mode, some of the advanced features were available, such as very efficient error trapping (the error trapping is utilized extensively when emulating CPUs other than the 6809, and performance is still better). One of the great advantages of a Z80 CPU over the 6500 series and 6800 series CPUs is it's built in memory management features, the 6309 not only had such features, it could transfer memory blocks in forward or reverse order to and from another memory locations and to or from I/O or even reverse memory in place (for flipping a graphic for instance).