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In digital logic, a hazard in a system is an undesirable effect caused by either a deficiency in the system or external influences. Logic hazards are manifestations of a problem in which changes in the input variables do not change the output correctly due to some form of delay caused by logic elements (NOT, AND, OR gates, etc.) This results in the logic not performing its function properly. The three different most common kinds of hazards are usually referred to as static, dynamic and function hazards. Hazards are a temporary problem, as the logic circuit will eventually settle to the desired function. Therefore, in synchronous designs, it is standard practice to register the output of a circuit before it is being used in a different clock domain or routed out of the system, so that hazards do not cause any problems. If that is not the case, however, it is imperative that hazards be eliminated as they can have an effect on other connected systems. ==Static hazards== A static hazard is the situation where, when one input variable changes, the output changes momentarily before stabilizing to the correct value. There are two types of static hazards: * Static-1 Hazard: the output is currently 1 and after the inputs change, the output momentarily changes to 0 before settling on 1 * Static-0 Hazard: the output is currently 0 and after the inputs change, the output momentarily changes to 1 before settling on 0 In properly formed two-level AND-OR logic based on a Sum Of Products expression, there will be no static-0 hazards. Conversely, there will be no static-1 hazards in an OR-AND implementation of a Product Of Sums expression. The most commonly used method to eliminate static hazards is to add redundant logic (consensus terms in the logic expression). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hazard (logic)」の詳細全文を読む スポンサード リンク
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