Method for managing data stored primarily in a read-only memory

#This application is a continuation of copending International Application No. PCT/DE01/03891, filed Oct. 11, 2001, which designated the United States and was not published in English.

#The invention relates generally to the field of semiconductor memories and methods for managing them. In this context, the invention relates particularly to a memory management logic unit for extended use of read-only memories.

#At present, programs are stored in microprocessor systems using, besides non-rewriteable read-only memories (ROMs), also rewriteable memories, such as RAMs or flash memories. In comparison with rewriteable memories, read-only memories can be produced inexpensively and, on account of easily implemented monolithic integration, afford faster access times and hence increased working speeds in the microprocessor systems. Since read-only memories are generally programmed using a mask for reasons of cost, it is not possible to alter their content again after manufacture. To be able to modify the stored data again after the memory has been manufactured too, rewriteable memories are also used instead of the read-only memories. These have the drawbacks over read-only memories described above, however.

#FIG. 1 is a block diagram showing a first embodiment of a memory management system according to the invention;

#FIG. 2 is a block diagram showing a second embodiment of the memory management system; and

#FIG. 3 is a schematic illustration of memory areas of a read-only memory and of a rewriteable memory and their association.

#Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a first inventive embodiment of a memory management system. In this case, a control unit 1 is connected to a read-only memory 3 and to a rewriteable memory 4. In addition, a memory management logic unit 2 controls access by the control unit 1 to the data in the read-only memory 3 and also the flow of data from the read-only memory 3 to the control unit 1.

#Some of the data in the read-only memory 3 have been replaced in this memory management system with data in the rewriteable memory 4. If the control unit 1 requests data having addresses that are in the read-only memory 3, the memory management logic unit 2 checks whether these addresses belong to the data which have been replaced with data in the rewriteable memory 4. If this is so, the memory management logic unit 2 blocks the flow of data from the read-only memory 3 to the control unit 1 and instead diverts access to the rewriteable memory 4. To this end, the addresses for the original access are replaced with the addresses for the corresponding area of the rewriteable memory 4.

#To be able to identify which memory areas of the read-only memory 3 have been replaced with memory areas of the rewriteable memory 4, the memory management logic unit 2 has, by way of example, access to an association table that lists the association between the replaced areas of the read-only memory 3 and the corresponding areas in the rewriteable memory 4. This association table is normally stored in the rewriteable memory 4 and from there is loaded into the memory management logic unit 2 before execution of the application program. It is then available in the memory management logic unit at a high access speed.