Since the offset is a 20 bit number the device can access up to 1 Mb of memory. The 64180's MMU lets the user segment the memory into up to three different areas. For instance, references to logical addresses 0 to 3FFFh could access physical addresses 0 to 3FFFh, references to 4000h to 7FFFh could access physical addresses 10000h to 13FFFh, and the last half of the logical space could access physical addresses 40000h to 47FFFh. Virtually any combination is possible. A more complete discussion of the MMU is beyond the scope of this article.
Many vendors have helpful application notes.
Some compilers even automatically support MMU, remapping it dynamically to let you code huge programs. Both Zilog and Toshiba sell a number of Z80-like devices with differing mixes of peripherals and memory. The range of processors grows daily. Both Toshiba and Zilog sell the 84013 and 84015, which are Z80 cores with conventional Z80 peripherals integrated on-board. In addition, the newer parts include a watchdog timer and clock generator.