Circuit Symbols and Diagrams | 电路符号与逻辑电路图

📚 Circuit Symbols and Diagrams | 电路符号与逻辑电路图

Circuit diagrams are the main tool for representing digital logic in CIE A-Level Computer Science. A diagram uses standard symbols for gates and lines for signals, so a Boolean function can be read visually. This revision note explains the symbols you must recognise, how to draw circuits from expressions, and how to analyse a diagram with truth tables and Boolean algebra.

电路图是 CIE A-Level 计算机科学中表示数字逻辑的主要工具。电路图使用标准符号表示逻辑门，使用连线表示信号，因此布尔函数可以被直观地读出来。这篇复习笔记解释你必须识别的符号、如何根据表达式绘制电路，以及如何用真值表和布尔代数分析电路图。

1. Why Standard Symbols Matter | 为什么标准符号很重要

In digital electronics, a logic gate symbol is not decoration; it is a precise contract. If a diagram uses a triangle with a small circle, it means inversion, not an amplifier. CIE exam questions expect you to recognise the standard shapes and to draw them unambiguously.

在数字电子技术中，逻辑门符号不是装饰，而是一种精确的约定。如果图中使用带小圆圈的三角形，它表示反相，而不是放大器。CIE 考试题要求你识别标准形状并清晰地画出来。

Using the same symbols allows designers, examiners and engineers to communicate without relying on a particular manufacturer. It also makes circuits easier to debug because the symbol shows the operation by shape, not by written label alone.

使用相同的符号可以让设计者、考官和工程师无需依赖特定制造商就能交流。它也让电路更容易调试，因为符号本身通过形状显示运算功能，而不仅仅依靠文字标签。

2. Signal Lines, Inputs and Outputs | 信号线、输入与输出

A signal line is drawn as a straight line, usually from left to right. The left side carries inputs such as A, B or C, and the right side produces the final output Y or Q. Each gate output feeds exactly one or more inputs unless a split is shown by a junction dot.

信号线画成直线，通常从左到右排列。左侧承载 A、B 或 C 等输入信号，右侧产生最终输出 Y 或 Q。每个门的输出连接到一个或多个输入，除非用连接点显示分支。

When two wires merely cross without a dot, they are not connected. A filled junction dot means an electrical connection. In most CIE logic diagrams, wires are drawn with right-angle bends and the signal flow is left to right.

当两条线只是交叉而没有圆点时，它们没有连接。实心连接点表示电气连接。在大多数 CIE 逻辑图中，连线使用直角转弯，信号流向通常从左到右。

Intermediate signals can be labelled with letters such as X, Y, S or C. This helps when a wire splits into several branches or when a complex diagram must be evaluated step by step.

中间信号可以用 X、Y、S 或 C 等字母标记。当一条线路分成多个分支，或者需要逐步分析复杂电路图时，这样做会很有帮助。

3. Basic Gate Symbols: NOT, AND, OR | 基本门符号：非门、与门、或门

The three fundamental gates are NOT, AND and OR. A NOT gate is a triangle ending in a small circle; it has one input and one output. The circle always means inversion.

三个基本门是非门、与门和或门。非门是一个末端带小圆圈的三角形；它有一个输入和一个输出。小圆圈始终表示反相。

An AND gate is drawn as a D-shaped body with a flat left side and rounded right side. It outputs 1 only when all inputs are 1. An OR gate has a curved left side and a pointed right side, outputting 1 when at least one input is 1.

与门画成 D 形，左边平直、右边呈圆弧形。只有当所有输入为 1 时，与门才输出 1。或门左边是弧形、右边是尖角，当至少一个输入为 1 时输出 1。