Method and apparatus for updating data in ROM using a CAM

Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition

Reexamination Certificate

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Details

C711S005000, C711S102000, C711S163000, C711S165000

Reexamination Certificate

active

07861030

ABSTRACT:
A method for providing field updates through the use of a memory emulation circuit with a content addressable memory (CAM) as the intelligent portion of the emulation circuit's arbiter. CAM circuit200is comprised of configurable memory and is initially unprogrammed. Address requests are passed straight through multiplexer201to Read Only Memory (ROM)202. As a result the data in the data location in ROM202that corresponds to the requested address will be output to data bus205. If data locations in ROM202become defective or contain data that needs to be upgraded the circuit implements a remapping of the data location. CAM circuit200is programmed with direct addresses to be replaced in ROM202. The direct addresses are paired to emulation addresses of data locations in configurable memory203. Upgraded or substitute data is programmed into the configurable memory203at the paired emulation address. When address requests are received thereafter, CAM circuit200compares the address request to its stored direct addresses. If a match is found the paired emulation address is passed through multiplexer201instead of the direct address. As a result, the substitute or upgraded data in configurable memory203is output to data bus205in place of the old data.

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