| 摘要 |
<p>PURPOSE:To avoid such a trouble where a secrecy protection state is unjustly released due to the nonstandardized power supply voltage, by using the signal sent from a power supply voltage detecting circuit to inhibit the output of the protection information held by a nonvolatile memory element for security. CONSTITUTION:The unjust release of a secrecy protection state due to the application of the nonstandardized voltage is avoided. For instance, a power supply voltage detecting transistor TR21 conducts earlier than a security TR11 set under a writing state when the power supply voltage Vcc is increased higher than the maximum rated level. Then one of both inputs of a logic gate 23 is always kept at 'L' and the output of the gate 23 is set at 'L' regardless of the other input. Thus a switching TR54 is turned off. As a result, the external reading operation of the stored information is inhibited regardless of a written or unwritten state of the TR11 in case the Vcc exceeds the rated level.</p> |
