Importance

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Abstract

An apparatus for use in a computer software protection system includes a protection device and a key externally connected thereto. The key includes a resistor and capacitor connected in series. The protection device includes an I/O port connected to the key such that a charge on the capacitor corresponds to a voltage on the I/O port. The I/O port is connected, selectively to ground by an NMOS switch, which is controlled by a control signal from a control program executing on a main game machine. The protection device further includes a voltage comparator having an input connected to the I/O port, and an output connected to an I/O interface that interfaces the protection device to the game console. In operation, the control program determines whether the key has a valid charging characteristic, as determined by the selection of the resistor and capacitor. While the control signal is unasserted, the NMOS switch is off, and the capacitors fully charged through the resistor. The control program temporarily switches on the NMOS switch to discharge the capacitor, upon which time control program discontinues the control signal. The voltage comparator then monitors the subsequent charging of the capacitor through the resistor. When a threshold voltage is reached, its output changes state. The program reads the charging time through the I/O interface, and uses the charging time as the basis for executed the protected computer software.

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First Claim