Security for digital signal processor program memory

Claim 1

A microprocessor adapted to provide security with respect to information contained in internal processor memory during execution from an external program memory, comprising internal program memory means for storing a program to be executed by said processor with respect to incoming signals to said processor, said internal program memory means being adapted to be reprogrammed and read repeatedly in response to receipt of write and read instructions therefor, processing means for receiving and processing said incoming signals in accordance with said program, and security means for providing two levels of security against access to information contained in said internal program memory, said security means including means for generating a security signal when the internal program memory is to be made secure, means responsive to said security signal for selectively preventing access to said internal program memory upon receipt of write or read instructions therefor by said microprocessor from a source external to said microprocessor, and means further responsive to said security signal for selectively disabling execution of any program from a source external to said microprocessor.