时序逻辑设计实践 (Sequential Logic Des

时序逻辑设计实践 (Sequential Logic Design Practices)
The purpose of this chapter is to familiarize you with the most
commonly used and dependable sequential-circuit design
methods. Therefore, we will emphasize synchronous systems, that
is, systems in which all flip-flops are clocked by the same,
common clock signal. Although it’s true that all the world does not march to
the tick of a common clock, within the confines of a digital system or
subsystem we can make it so. When we interconnect digital systems or
subsystems that use different clocks, we can usually identify a limited
number of asynchronous signals that need special treatment, as we’ll show
later.
We begin this chapter with a quick summary of sequential circuit
documentation standards. After revisiting the most basic building blocks of
sequential-circuit design—latches and flip-flops—we describe some of the
most flexible building blocks—sequential PLDs. Next we show how
counters and shift registers are realized in both MSI devices and PLDs, and
show some of their applications. Finally, we show how these elements come
together in synchronous systems and how the inevitable asynchronous