| 摘要 |
An internal ROM of a CPU holds a plurality of check start addresses, skip values and storing addresses. An external ROM holds a check sum in each of the storing addresses, where each check sum is calculated for each route determined by each combination of check start address and skip value. To check the external ROM, data from retrieval addresses that are determined by a selected combination of check start address and skip value are read and a check sum is calculated and compared with the check sum stored in the appropriate storing address. If these values tally, the external ROM is judged to be normal. The check sums in the storing addresses may be coded by exclusively OR-ing them with some code data. |
