| 摘要 |
PROBLEM TO BE SOLVED: To detects the abnormality of memory control of an address counter, etc., in cell copy control by predicting the sequence number of a next copy cell from the sequence number of detected copy cells and the number of sheets of the cell copies so as to compare them with the sequence number of the next copy cell. SOLUTION: First, an adder circuit 2 adds a sequence number to the unused area of a cell over head(COH) for each cell. The sequence numbers of the cells of copied N cells have the same numbers continuously N times by a cell copy circuit 1. A monitoring circuit 3 detects the abnormality of cell copy control by a sequence number comparing device 7. After detecting the copy cell, the device 7 compares the sequence number Z of a detected cell and a counted value Y of a sequence counter 6 showing the previously predicted sequence number with each other. When the comparison shows squality, cell copy control is judged to be normal but when the comparison shows inequality, cell copy control is judged to be abnormal.
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