| 摘要 |
<p>PURPOSE:To prevent the deterioration of a characteristic in ROM owing to excessive writing by prohibiting the supply of a write voltage and the like after it is supplied to EPROM formed by means of dual gate transistors (TR) for prescribed time. CONSTITUTION:A timer TM provided in a timing control circuit CONT is started when a program signal, the inverse of PGM comes to L in a state where a write high voltage Vpp is impressed, a chip enable signal, the inverse of CE comes to L, an output enable signal, the inverse of OE to L. Then, the write voltage for the dual gate EPROM elements Q1-Q6 having control gates and floating gates whose write voltage is selected by setting an internal write signal, the inverse of We to be L when timer time elapses, is prohibited. It is the same for a deletion voltage, and the deterioration of the characteristic in the EPROM elements owing to the supply of the excessive voltage can be prevented.</p> |
