Apparatus for safeguarding data entered into a microprocessor
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United States of America Patent
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-
Feb 7, 1984
Grant Date -
N/A
app pub date -
Jul 7, 1981
filing date -
Sep 13, 1980
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
For any given program entered into an EPROM in a microprocessor, read-out from certain storage locations or cells in the EPROM is prevented by transmission gates connected into externally accessible data lines. Transmission through the transmission gates is blocked by the arithmetic unit when a blocking command is present in one or more cells of the EPROM. These commands are only entered into the EPROM after all information required for the program is stored in the latter and, if necessary, the unit has been tested for proper operation. When the program is erased, the blocking commands are also erased so that the chip is available for another application.
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