| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable check circuit capable of quickly detecting CPU runaways, etc., without influencing the operations of a CPU. SOLUTION: A latch 101 receives counting values CNT from a program counter 120 for the CPU. A comparison circuit 102 compares the counting values CNT, with the boundary values BDY1 stored into a boundary value storage part 104 and a comparison circuit 103 compares the counting values CNT with boundary values BDY2 stored into a boundary value storage part 105. A gate 108 outputs '0' as a determination signal JDG, when the counting values CNT lie within a range decided by the boundary values BDY1 and BDY2, but otherwise outputs '1'. A gate 109 outputs the determination signal JDG, as it is, or in reverse, according to values stored into a mode graph storage part 106 and a gate 110 outputs the determination signal JDG to the outside, only when values stored into a function valid/invalid flag storage part 107 are '1'.
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