| 摘要 |
<p>PURPOSE:To attain substantial content changes for a prescribed number of times without ultraviolet ray erasure requiring an expensive case by using a content written on in the 2nd ROM to change the storage area of the 1st PROM accessed by an external address. CONSTITUTION:In writing the 1st data on the 1st PROM 11, the 2nd PROM 12 is kept unwritten, an output 1 from the PROM 12 is kept to an internal address terminal a13 of the ROM 11 and data is written on the designated stor age area based on the write address fed to external address terminals A0-A12. Ahead the write of the 2nd data, 0 is written from a write terminal SD to the 2nd PROM 12. As a result, an output 0 is being supplied from the PROM 12 to the internal address terminal a13 of the PROM 11 and data is written on a different storage area based on the write address fed to the external address terminals A0-A12 together with the supply of 0. Thus, substantial rewrite of (p-1) times is applied by supplying a high-order p bits from the 2nd PROM.</p> |
