| 摘要 |
<p>PURPOSE:To prevent the increase of probability for the defective state of a microcomputer itself by providing a function to substitute a built-in RAM or a RAM connected externally to the microcomputer that has a defective part with another RAM. CONSTITUTION:A CPU 101 is provided together with an address deciding circuit 102, a switch circuit 103, a RAM(1) 104, a RAM(2) 105, an I/O bus 106, an address bus 107, and the data buses 108 and 109. Then a built-in RAM or an external RAM is tested. If these RAMs have the defective parts, they are replaced with another built-in RAM. Thus the defect of the RAM can be evaded. As a result, the number of defective microcomputers can be decreased despite the presence of defective built-in RAMs. Then it is possible to offer a microcomputer having a built-in RAM of large capacity to a user at a low cost.</p> |
