| 摘要 |
PURPOSE:To easily attain surer security by providing a comparing circuit which compares the value of one of plural passwords, which is addressed by a first field, with an ciphered value and permitting the access from the external to a PROM only at the time of coincidence between them. CONSTITUTION:Plural passwords are stored in a PROM 5, and a test circuit 17 is provided with a shift register 20 where data which is inputted from the external and consists of first and second fields are temporarily stored in serial, a ciphering circuit 21 which ciphers data of the second field, and a comparing circuit 22 which compares the value of one of plural passwords addressed by the first field with the value ciphered by the ciphering circuit 21, and the access from the external to the PROM 5 is permitted only when this comparison results in coincidence. Thus, invalid data access is inhibited to realize the security of high level. |
