Program Debugging 199 give an MSR of 100% or 0%, but stops one step short of the maximum and minimum. Since there are 255 steps altogether, the step size is less than 1%. The circuit should also be tested for fail-safe operation, that is, no unplanned or potentially dangerous output is caused by an incorrect input operating sequence. In this case, operating both the `Up' and `Down' buttons together would be an erroneous input combination, which should result in no change in speed, because the increment and decrement operations cancel out. Other examples of potential problems that would need to be considered are input switch bounce, variation in component performance (check specifications), dynamic operation of motor, minimum MSR required to make the motor run, and so on. Complex applications are likely to have more potentially incorrect input conditions and component-related problems, but the test schedule should ideally anticipate all possible fault modes (not easy!). If the circuit is being produced on a commercial basis, a formal test schedule would be needed, and the performance certificated as being correct to the product specification. A basic test schedule for the MOT1 program running in a PIC 16F84A has already been outlined for the simulator test in Table 9.2, and this can be adapted for hardware testing. Additional documentation should be prepared according to circumstances (education,