A flexible address mapping method and mechanism allows mapping regions of a microcontroller's memory and I/O address spaces for a variety of applications by defining memory regions which are mapped to one of a set of physical devices by a programmable address mapper controlled by a set of programmable address registers. The mapping allows setting attributes for a memory region to prohibit writes, caching, and code execution. A deterministic priority scheme allows memory regions to overlap, mapping addresses in overlapping regions to the device specified by the highest priority programmable address register.