Detection of improper CPU operation from lap time pulses and count of executed significant steps

A monitoring apparatus for monitoring a central processing unit, said central processing unit performing a main operation and not performing a monitoring operation, said main operation including repeatedly executing a program containing a plurality of significant steps, said central processing unit producing a lap time pulse having leading and trailing edges corresponding respectively to successive executions of said program and producing a step-related signal indicative of whether said significant steps are successfully executed, the apparatus comprising:

• means for receiving said lap time pulse from said central processing unit;
• means for receiving said step-related signal from said central processing unit;
• and
• monitoring means for performing said monitoring operation, not performed by said central processing unit, without interrupting said main operation of said central processing unit, said monitoring means comprising
• program execution diagnostic means for determining whether said lap time pulse has a duration between a maximum value and a minimum value, and generating a program execution alarm signal when said duration is determined to not be between said maximum value and said minimum value,
• step execution diagnostic means for examining said step-related signal and determining whether said central processing unit has unsuccessfully executed a predetermined number of said significant steps when said central processing unit has repeatedly executed said program a predetermined number of times, and generating a step execution alarm signal if said central processing unit is determined as having unsuccessfully executed said predetermined number of significant steps and
• an alarm responsive to said program execution alarm signal and said step execution alarm signal.