Read-only memory having a security circuit preventing unauthorized

Abstract

A read-only memory provides a security circuit capable of nullifying data being output from the read-only memory itself, a memory cell array consisting of memory cells arranged in matrix, an input driver for receiving and amplifying address signals sent from a CPU, a decoder for specifying a memory cell included in the memory cell array in response to address signals sent from the input driver, and an output buffer for temporarily storing storage data of the memory cell and sending to the security circuit. The security circuit is used for inhibiting impermissible copying of memory data of the read-only memory. It serves to nullify the data read out of the read-only memory unless a memory address for specifying the data being output meets a predetermined address. That is, the security circuit can disable all of the address signals or one of the address signal when a predetermined address is accessed in the impermissible data copying operation.