| 摘要 |
<p>PURPOSE:To retain secrecy by utilizing the fact that the EPROM (erasable ROM) cell of FAMOS (floating gate avalanche injection MOS circuit) construction is of a ultraviolet ray erasing type, so that make reading of stored data from the outside impossible. CONSTITUTION:Flag 3 composed of an EPROM cell of FAMOS construction is installed separately from EPROM cell group 1 of FAMOS construction. When flag 3 is under erased condition, data written on FAMOS cell group 1 can be read from output line 7. Moreover, when the write signal is given to flag 3 from write line 4 and flag 3 is set under the writing condition, reading of data of EPROM cell group 1 is prohibited and the data are not transmitted to output line 7. To read out the data from the outside, flag 3 must be set to an erased condition. If an ultraviolet ray is irradiated for this purpose, all pieces of information in EPROM cell group 1 which are the original data, are erased at the same time. Thus, secrecy information stored in cell group 1 is retained.</p> |
