| 摘要 |
PURPOSE:To protect data and to send information on the occurrence of a hardware fault, by counting the number of reset pulses from a watch dog circuit, discriminating that a hardware fault occurs when the counted value exceeds a prescribed value, and inhibiting access to the memory. CONSTITUTION:The output signal ''e'' of a watch dog circuit 10 whose output signal ''e'' is inverted in level when an input pulse signal ''a'' is interrupted for a prescribed time or longer is supplied as a reset signal to a computer. At this time, if a program runaway due to a hardware fault occurs, the signal ''e'' is outputted repeatedly, so an N frequency dividing counter 16 counts the signal ''e'' up to a prescribed number and then a signal ''f'' is inverted to a level H. Then, the output of an NOR circuit 15 goes down to a level L and a clock input to the counter 16 is ceased to protect an output ''H'' invariably at H. This output signal ''f'' is inputted to a memory access inhibiting circuit and an LED lighting circuit to protect data and also inform the occurrence of the program runaway to the operator. |
