3.5.1 confirmation<br>Each key is a mechanical switch. After pressing the key, it is necessary to determine whether the key is pressed and whether the key is closed depends on the high and low levels. Because it is a mechanical switch, voltage vibration usually occurs when the shock is turned off or on, which is likely to cause button failure. Therefore, anti shake button technology is needed.<br>3.5.2<br>The hardware method of the anti shake key technology is to add a NAND circuit to the key circuit. The basic digital component of the electronic technology shows that this key will not affect the key value in the case of jitter; the method is to add a noise reduction circuit on the top, but in many main circuits, it is not easy to implement, and the circuit is redundant. Therefore, it is usually applicable when the number of keystrokes is small.<br>3.5.3 key protection<br>There are special circumstances due to the design itself. Therefore, for special cases of circuit, we must be perfect. In the process of operation, it is inevitable to encounter two or more keys. If this situation is not considered, the key position may fail or even cross. We need to define more logic functions, and put the circuit out of reasonable and normal operation, or to be disconnected or in high resistance state. Press a key in each round without limiting the time range. By default, the system only generates program functions.<br>
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