| 摘要 |
<p>PURPOSE:To prevent illegal access to a secret zone by comparing the address value of one of passwords with a value stored in a shift register and allowing access to a PROM only when they match each other. CONSTITUTION:Plural passwords are stored in the secret zone 5a of the PROM (Programmable Rom) 5 used as a data memory before ad a password read out of the PROM 5 corresponding to the frequency of input of a password which is inputted from outside is selected; and the value of the password is operated and compared with data inputted to the shift register 20 and only when they match each other, a test mode is allowed by a test circuit 17. Consequently, illegal data access which is caused when data access to the conventional secret zone is freely performed since the test mode is realized is inhibited and high-level security is realized.</p> |
