PURPOSE:To attain inexpensive checker, by writing the content of an ROM into an RAM for checking the operation of the ROM relevant to the operating condition of the ROM. CONSTITUTION:An address counter 8 receiving a clock gives an address of a static RAM 9 and the ROM 11 to be measured at the write check mode and writes all the content of the ROM 11 to be measured to the static RAM 9. Each bit is compared with a comparison check circuit 13 in a comparatively slow clock timing after the end of write. Thus, the check of the ROM operation relevant to the change in the operating condition of the ROM is attained easily without other input medium.
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