Arrays, linked lists, and strings all provide simple ways to structure data sequentially. They provide a first level of abstraction that we can use to group objects in ways amenable to processing the objects efficiently. Having settled on these abstractions, we can use them in a hierarchical fashion to build up more complex structures. We can contemplate arrays of arrays, arrays of lists, arrays of strings, and so forth. 继续阅读“Elementary Data Structures ~ Compound Data Structures”
Elementary Data Structures ~ Strings
We use the term string to refer to a variable-length array of characters, defined by a starting point and by a string-termination character marking the end. Strings are valuable as low-level data structures, for two basic reasons. 继续阅读“Elementary Data Structures ~ Strings”
信号完整性小记 ~ 串扰
串扰是发生在一个信号与返回路径和另外一个信号与返回路径之间的效应，是不同传输线之间的能量耦合。当不同结构的电磁场相互作用时，就会产生串扰。不只是在信号路径上，返回路径也会产生串扰。 继续阅读“信号完整性小记 ~ 串扰”
Relational Databases ~ Introduction to SQL IV
SQL provides a mechanism for nesting subqueries. A subquery is a select-from-where expression that is nested within another query. 继续阅读“Relational Databases ~ Introduction to SQL IV”
Relational Databases ~ Introduction to SQL III
The SQL operations union, intersect, and except operate on relations and correspond to the mathematical set-theory operations ∪, ∩, —. We shall now construct queries involving the union, intersect, and except operations over two sets. 继续阅读“Relational Databases ~ Introduction to SQL III”
Relational Databases ~ Introduction to SQL II
The basic structure of an SQL query consists of three clauses: select, from, and where. The query takes as its input the relations listed in the from clause, operates on them as specified in the where and select clause, and then produces a relation as the result. 继续阅读“Relational Databases ~ Introduction to SQL II”
Elementary Data Structures ~ Linked Lists II
Linked lists bring us into a world of computing that is markedly different from that of arrays and structures. With arrays and structures, we save an item in memory and later refer to it by name (or by index) in much the same manner as we might put a piece of information in a file drawer or an address book; with linked lists, the manner in which we save information makes it more difficult to access but easier to rearrange. Working with data that are organized in linked lists is called list processing. 继续阅读“Elementary Data Structures ~ Linked Lists II”
信号完整性小记 ~ 反射
1、反射问题概述
1.1 反射的产生
只要信号遇到瞬时阻抗突变，反射就会发生。反射可能发生在线的末端，或者是互联拓扑结构改变的地方，如拐角、过孔、T 型结构、连接件和封装处。为了保持信号的完整性，互联设计时要尽可能保持互联阻抗的恒定。 继续阅读“信号完整性小记 ~ 反射”
晶体三极管驱动继电器电路及其抗干扰的一些建议
1、连接方法
用晶体三极管驱动继电器时，建议连接集电极使用。另外，继电器为 ON 时外加额定电压、继电器为 OFF 时使电压为零是一种避免故障的使用方法。并且，在低电压线路（5V 以下）中，请选择考虑到晶体三极管电压降落的电源电压、继电器品种。（在 5V 线路中，建议使用线圈额定电压为 4.5 V型） 继续阅读“晶体三极管驱动继电器电路及其抗干扰的一些建议”