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US 6,295,590 B1Granted
Semiconductor memory apparatus having a protecting circuit
AssigneeRohm Col, Ltd.
InventorKyoji Marumoto
Life of this patent
Estimating the term…
Abstract
A semiconductor memory incorporates a protecting circuit which causes data, stored in a memory portion, to be output by executing a key canceling sequence from an external apparatus. The data stored in the memory are output only when a key canceling signal is input to the protecting circuit. Thus the data are not output only by inputting an address signal and a reading signal to the memory apparatus. As a result, it is impossible to find out the contents of the program stored in the memory portion without inputting the key canceling signal.
Claims4
A semiconductor memory apparatus, comprising:
- a memory portion storing a program;
- a terminal for external connection;
- a three-state buffer, one end of said three-state buffer is connected to said memory portion so that said three-state buffer can receive program data from said memory portion, and another end of said three-state buffer is connected to said terminal for external connection, said three-state buffer being capable of taking a high-impedance state in addition to two-value states of high-level and low-level;
- a key memory for storing key data;
- an input register, connected to said terminal for external connection, for storing a key release signal received via said terminal when said three-state buffer is in the high-impedance state;
- an RS flip-flop connected to said three-state buffer, for turning said three-state buffer into the high-impedance state to disconnect said memory portion from said terminal under a reset state and for canceling the high-impedance state under a set state;
- a power-on reset circuit for resetting said RS flip-flop when a power is turned on;
- and
- a comparator for comparing an output from said key memory and an output from said input register to set said RS flip-flop when the two outputs coincide.
6 more elements
Dependencies are inferred from the claim text.