| 摘要 |
<p>PURPOSE:To obtain a mask ROM for relieving a defective bit with a simple circuit constitution without enlarging a chip size by using a EPROM cell. CONSTITUTION:Defectives of bit lines and defective parts of group bits found by a test result of a mask ROM section 1 are previously written in a defective output writing circuit 32, outputted to a error correction circuit 31, and defective parts are relieved by using parity. The writing circuit 32 is enough to be a EPROM having the number of bits corresponding to defective parts and small capacity is sufficient for the purpose. An address of a defective part of a word line found by a test result of the mask ROM 1 is written in a word line defective address writing circuit 33, when it coincides with an external access address, data from a corresponding EPROM 2 for redundancy is substituted for data from the ROM 1, and outputted. A defective for a single bit is relieved by either of the correcting circuit 31 or the PROM 2 for redundancy. Thus, since suitable methods relieve defective parts respectively, the mask ROM chip size.</p> |
