Microcontroller having dedicated hardware for memory address space

Abstract

A microcontroller is presented including additional hardware which generates multiple auxiliary address signals needed to expand the memory address space of the microcontroller. The auxiliary address signals allow access to memory locations within external memory devices which would not otherwise be accessible while advantageously maintaining software compatibility with previous microcontroller products. The auxiliary address signals form the most significant bits of augmented addresses, thereby dividing memory locations within the external memory devices into multiple memory banks of equal size. When memory banking is enabled, software instructions select the desired memory bank by writing appropriate values to address bit positions within a memory banking control (MBC) register. The auxiliary address signals are normally produced having values stored within corresponding bit positions of the MBC register. When address signals are generated which correspond to a portion of the memory address space reserved for operating system software, however, the additional hardware modifies the auxiliary address signals such that a selected memory bank is always accessed. As a result, operating system software need only be present in the selected memory bank. This method of generating the auxiliary address signals eliminates the need to duplicate operating system software in each memory bank mapped to a reserved portion of the memory address space, allowing efficient utilization of the external memory devices.