Microcontroller having dedicated hardware for memory address space expansion supporting both static and dynamic memory devices

摘要

A microcontroller is presented including additional hardware which generates additional address signals needed to expand the memory address space of the microcontroller. The additional 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 most significant address signals divide memory locations within the external memory devices into multiple memory banks of equal size. The remaining least significant address signals are used to access memory locations within each memory bank. When memory banking is enabled, software instructions select the desired memory bank by writing appropriate values to address bit positions within one or more memory banking registers. In a first embodiment, additional "auxiliary" address signals have values stored within corresponding bit positions of a memory banking control (MBC) register. A second embodiment includes the ability to generate multiplexed address signals for DRAM devices, and to generate the multiplexed address signals such that variably sized DRAM devices are easily accommodated. When address signals are generated which correspond to a portion of the memory address space reserved for operating system software, the additional hardware modifies the additional 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. Elimination of the need to duplicate operating system software in each memory bank mapped to a reserved portion of the memory address space allows efficient utilization of the external memory devices.