嵌入式硬件 Jack Ganssle

　　英文版的嵌入式硬件， embedded hardware， 一本关键嵌入式开发硬件学习的书

　　1.1 Lesson One on Hardware： Reading Schematics This section is equally important for embedded hardware and software engineers. Before diving into the details， note that it is important for all embedded designers to be able to understand the diagrams and symbols that hardware engineers create and use to describe their hardware designs to the outside world. These diagrams and symbols are the keys to quickly and effi ciently understanding even the most complex hardware design， regardless of how much or little practical experience one has in designing hardware. They also contain the information an embedded programmer needs to design any software that requires compatibility with the hardware， and they provide insight to a programmer as to how to successfully communicate the hardware requirements of the software to a hardware engineer.

　　Regardless of the type， to understand how to read and interpret these diagrams， it is important to fi rst learn the standard symbols， conventions， and rules used. Examples of the symbols used in timing diagrams are shown in Table 1.1， along with the conventions for input/output signals associated with each of the symbols. An example of a timing diagram is shown in Figure 1.1. In this fi gure， each row represents a different signal. In the case of the signal rising and falling symbols within the diagram， the rise time or fall time is indicated by the time it takes for the signal to move from LOW to HIGH or vice versa （the entire length of the diagonal line of the symbol）。 In comparing two signals， a delay is measured at the center of the rising or falling symbols of each signal being compared. In Figure 1.1， there is a fall time delay between signals B and C and signals A and C in the fi rst falling symbol. In comparing the fi rst falling symbol of signals A and B in the fi gure， no delay is indicated by the timing diagram.