Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Patent
1995-10-06
1998-04-07
An, Meng-Ai T.
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
395186, 395490, G06F 1214
Patent
active
057377600
ABSTRACT:
A microcontroller (20) provides security for internal instructions and data while allowing instruction fetches to external, off-chip memory connected to an expansion bus (30). A central processing unit (CPU) (21) provides a load instruction register signal to indicate when an access is an instruction fetch. When the load instruction register signal is active while the address is within the range of an on-chip nonvolatile memory (25), a security logic circuit (40) is reset to a first state. In this first state, the security logic circuit (40) also allows non-instruction fetches from the nonvolatile memory (25). However when the load instruction register signal is active while the address is not within the range of the nonvolatile memory (25), the security logic circuit (40) is set to a second state. While in this second state, the security logic circuit (40) disables attempted accesses to the nonvolatile memory (25). The security feature is selectively enabled or disabled as determined by a configuration register (23).
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Grimmer, Jr. George G.
Rhoades Michael W.
An Meng-Ai T.
Motorola Inc.
Polansky Paul J.
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