| 摘要 |
PURPOSE:To protect the security of data written in an EPROM to improve the security by providing a protecting circuit and writing data in at least one of plural protection bits in this protecting circuit. CONSTITUTION:A single chip microcomputer provided in a circuit block 20 consists of a microprocessor 1, an EPROM 2, a protecting circuit 3, input/output ports 4 and 5, etc., and they are connected mutually through an address bus AB and a data bus DB. Memory cells D1 and D0 as protection bits are provided in the circuit 3 and are set to '1' in the initial state. After data is written in each address of the EPROM 2, '0' is written in at least one of bits D1 and D0 to make it impossible that data is read out from the external through signal control gates G1-G6. Thus, the security of data written in the EPROM 2 is protected to improve the reliability of security. |
