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微处理器之所以能够有条不紊地执行程序中的各条指令,全靠控制器在一定的时间里发出相应的操作。完整地执行一条指令所需的时间称为指令周期。在早期的计算机中,为了简化,多采用同步控制,即规定各个不同的指令具有相同的指令周期。无疑,这种方法的时间利用率不高,速度较低。现代的微型机多采用异步控制或准同步控制,特别是后者。所谓异步控制,即根据不同指令确定不同的指令周期,不设统一的标准长度。显然,这种方法快速有效,但控制较为复杂。目前最为常用的方法是介于同步和异步之间的准同步控制,即每个指令周期由1～5个机器周期组成,而每个机器周期再由3～6个状态(即时钟周期)组成。这种方法集前面两种方法的优点子一处,效率较高而又比较规则。因而,本文将重点讨论这种典型的时序及其设计方法。
The reason why the microprocessor can orderly execute each instruction in the program depends entirely on the controller to issue the corresponding operation in a certain period of time. The time required to fully execute an instruction is called the instruction cycle. In earlier computers, for simplicity, synchronous control was often used, meaning that each different instruction had the same instruction cycle. Undoubtedly, this method of time utilization is not high, the speed is low. Modern micro-multi-use asynchronous control or quasi-synchronous control, especially the latter. The so-called asynchronous control, that is, according to different instructions to determine different instruction cycles, there is no uniform standard length. Obviously, this method is fast and effective, but the control is more complicated. At present, the most commonly used method is between quasi-synchronous control of synchronization and asynchronization, that is, each instruction cycle consists of 1 to 5 machine cycles, and each machine cycle is composed of 3 to 6 states (that is, clock cycles) . This method combines the advantages of the previous two methods in one, more efficient and more rules. Therefore, this article will focus on this typical timing and design methods.