电气专业英语课文翻译(4)

Output interfaces take a similar form (Fig.18.2), the biopic difference being that here the flow of information is in the opposite direction; it is passed from the program to the outside world. In this case the program may call an output subroutine which supervises the operation of the interface and performs the scaling numbers which may be needed for a digital-to-analog converter (DAC) .This subroutine passes information in term to an out analog form using a DAC .Finally the signal is conditioned (usually amplified ) to a form suitable for operating an actuator.

输出接口采用相似的形式，明显的差别在于信息流的方向相反；是从程序到外部世界。这种情况下，程序可称为输出程序，它监督接口的操作并完成数字模拟转换器所需数字的标定。该子程序依次送出信息给输出器件，产生相应的电信号，由DAC转换成模拟形式。最后，信号经调理（通常是放大）以形成适应于执行器操作的形式。

The signals used within microcomputer circuits are almost always too small to be connected directly to the ―outside world ‖and some king of interface must be used to translate them to a more appropriate form .The design of section of interface circuits is one of the most important tasks facing the engineer wishing to apply microcomputers. We have seen that in microcomputers information is represented as discrete patterns of bits ;this digital form is most useful when the microcomputer is to be connected to equipment which can only be switched on or off, where each bit might represent the state of a switch or actuator.

在微机电路中使用的信号几乎总是太小而不能直接连接到外部世界，因而必须用某种形式将其转换成更适宜的形式。接口电路部分的设计是使用微机的工程师所面临最重要的任务之一。我们已经了解到微机中，信息以离散的位形式表示。当微机要与只有打开或关闭操作的设备相连接时，这种数字形式是最有用的，这里每一位都可以表示一开关或一执行器的状态。

Care must be taken when connecting logic circuits to ensure that their logic levels and current ratings are compatible .The output voltages produced by a logic circuit are normally specified in terms of worst case values when sourcing or sinking the maximum rated currents .Thus VOH is the guaranteed minimum ―high ‖ voltage when sourcing the maximum rate ―high‖ output current IOH ,while VOL is the guaranteed ―low‖ output voltage when sinking the maximum rated ―low ‖output current IOL .There are corresponding specifications for logic inputs which specify the minimum input voltage which will be recognized as a logic ―high‖ state VIH ,and the maximum input voltage which will be regarded as a logic ―low‖ state VIL.

连接逻辑电路时，必须小心翼翼，以保证他们的逻辑电平和电流额定值是兼容的。有逻辑电路产生的输出电压通以拉出或灌入最大额定电流时，按最弱情况下数值所定义。这样VOH是当拉出最大额定高输出电流IOH时所允许的最小高电压。而VOH则是当灌入最大额定地输出电流IOL时所允许的最低电压。对逻辑输入也有相应的参数，规定最小输入电压为逻辑高状态VIH,以及最大输出电压为逻辑低状态VIL。

For input interface, perhaps the main problem facing the designer is that of electrical noise .Small noise signal may cause the system to malfunction, while larger amounts of moist can permanently damage it. The designer must be aware of these dangers from the outset. There are many methods to protect interface circuits and microcomputer from various kinds of noise .Following is some examples:

Input and output electrical isolating between the microcomputer system and external devices using an opt-isolator or a transformer.

1.Removing high frequency noise pulses by a low-pea filter and Schmitt-trigger.

1.Protecting against excessive input voltages using a pair of diodes to power supply reversibly biased in normal direction.

对于输入接口，也许设计所面临的主要问题是电噪声，小噪声信号会引起系统工作不良，而大量的噪声会造成永久性的损坏。设计者必须从一开始就清楚这些危险。有许多方法保护接口电路和微机不受各种各样的噪声影响下面是一些例子： 1，使用光电隔离或变压器实现微机系统和外部器件之间的输入输出电信号隔离。 2用一低通滤波器和一施密特触发器排除高频噪声脉冲。3，用一对二级管以反向偏置于正常方向的形式连接至电源端，来保护过高的输入电压

For output interface, parameters VOH, VOL, IOH and IOL of a logic device are usually much to low to allow loads to be connected directly, and in practice an external circuit must be connected to amplify the current and voltage to drive a load. Although several types of semiconductor devices are now available for controlling DC and AC powers up to many kilowatts, there are two basic ways in which a switch can be connected to a load to control it : series connection and shunt connection as shown in Figure 18.3.

对于输出接口，一逻辑器件的参数VOL，VOH, IOL, IOH， 往往太小而不能直接与负载相连，实践中必须在一个外部电路将电流和电压进行放大以驱动一负载。现在尽管有一些类型的半导体器件可用于将DC和AC的功率控制若干千瓦，有两种基本方式将开关连至负载。如图的串联连接和并联连接。

With series connection, the switch allows current to flow through the load when closed, while with shunt connection closing the switch allows current to bypass the load.

Both connections are useful in low-power circuits, but only the series connection can be used in high-power circuits because of the power wasted in the series resistor R.

对于串联连接，开关闭合时使电流流过负载，而当并联连接时和上开关使电流绕过负载。两种方式都可用于低功率电路中，但只有串联连接才能用于高功率电路，这是因为串联电阻R上要消耗功率。

The field of communications is experiencing rapid and dramatic change. Traditionally, telecommunications has been the transmission of information over long distances by means of telephone, teletype, radio, or television. Data communications has been the exchange of data between computer-related devices. Today, these distinctions have blurred as the two have been converging into networks—a group of computers and other devices connected by communication facilities—in which information is processed and communicated in the form of sound, data, …… 此处隐藏：5058字，全部文档内容请下载后查看。喜欢就下载吧 ……