Circuit for Protection of ROM From Copying
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
In order to prevent piracy of software stored in read-only memory (ROM), a ROM chip includes a protective circuit consisting of a sequential logic circuit with latches and resistor capacitor (RC) components. The application of the correct sequence of code words enables the ROM, while an incorrect sequence of code words or delays sensed by RC time constants leaves the ROM disabled. A ROM-integrated circuit chip consists of a memory array with address lines as inputs and data lines as outputs. Another line, the Chip Enable (CE) line, when active, enables the data outputs. Typically, several ROMs share the same address lines and their data lines are connected to the same data bus. As the equipment containing the ROMs performs its function, the ROMs are activated, one at a time, through their CE lines, as shown in Fig. 1.