说明：  无沦是用离散逻辑、可编程逻辑，还是用全定制硅器件实现的任何数字设计，为了成功地操 作，可靠的时钟是非常关键的。设计不良的时钟在极限的温度、电压或制造工艺的偏差情况下将 导致错误的行为，并且调试困难、花销很大。 在设计PLD/FPGA时通常采用几种时钟类型。时钟可 分为如下四种类型：全局时钟、门控时钟、多级逻辑时钟和波动式时钟。多时钟系统能够包括上 述四种时钟类型的任意组合。
(without the expense of discrete logic, programmable logic, or a full-custom silicon device of any digital design, in order to successfully operate, reliable clock is very critical. The poor design of the clock, the limits of temperature, voltage or manufacturing process of the deviation would lead to wrong behavior, and debugging difficulties, costing much. The design PLD/FPGA usually use several types clock. The clock can be divided into the following four types : global clock, clock gating, multi-level logic clock and volatility clock. Multi-clock system to include the above four types of arbitrary clock portfolio.)