| 摘要 |
PURPOSE:To take easily measures against an unstable or incorrect operation of a CPU due to a frequency variation of a clock pulse by detecting a frequency abnormality of the clock pulse. CONSTITUTION:A test routine is provided on a part of a program, and in accordance with it, a counter is constituted in a CPU2, a clock pulse CK is divided by a frequency divider 4 and a clock pulse LCK is counted. This counting is executed only in a period in which a gate pulse SO is given. That is to say, when an address designating signal AD for generating a decoding output Q3 and a write signal WR are sent out, an output of an AND gate 8c is converted to ''H'', by which a pulse generator 9 genertes as ''H'' a gate pulse of a prescribed time width. In accordance with the end of the gate pulse SO, a count value of this time is compared with the upper limit frequency value and the lower limit frequency value of the divided clock pulse LCK, and in accordance with it, whether the frequencyh of the clock pulse CK is abnormal of normal is decided, and if it is abnormal, an operation of the CPU2 is stopped, or a measure for sending out an alarm, etc. is executed. |
