| 摘要 |
PURPOSE:To diagnose faults of all functions of an ECC circuit by providing a means which gives diagnostic data to the ECC circuit and inhibits the write of redundant bits, which are generated in the ECC circuit, to a memory in accordance with diagnostic data when the ECC circuit is diagnosed. CONSTITUTION:A check bit memory 3 is provided with a write inhibit terminal, and a write inhibiting signal is applied to the inhibit terminal when an ECC circuit 4 is checked. A diagnostic flag register 17 is provided in a memory control circuit 5, and the output of an OR gate 19 is inputted to a write/read command terminal WE of the check bit memory 3, and the terminal WE has the function of the write inhibiting signal. When the terminal WE is turned ON, input data 25 and 26 are written in memories 2 and 3. If the diagnostic flag 17 is turned ON to set the diagnostic mode, a diagnostic mode signal 18 is turned ON, and as the result, the gate 19 is closed, and WE (CHECK BIT)-N 22 is turned OFF, and data is not written in the check bit memory 3. Thus, operations for all erroneous patterns which an error detecting circuit can detect are diagnosed. |
