问题 写作题

Section C

Directions: Write an English composition according to the instructions given below in Chinese.

请你从你父母、老师或同学中选择一位做你的知心朋友,说明你的理由。

要求:1. 词数不少于120;

2.不能写出你的真实姓名与学校名称;

答案

If I must choose one person from my classmates ,my teachers and my parents as my best friend,I'd

Like to select my father。

The reasons are as follows 。Firstly ,my father is more than my father ,he not only takes good care of my life but also pays close attention to my studies,we often have face-to face talks on many problems such a how to form good habits ,how to study effectively,how to keep healthy and so on 。Secondly,he is kind and patient 。When I make mistakes,he helps me look for reasons so that I can benefit from them。Thirdly,he shares some interests with me ,we often play badminton,table tennis ,watch TV together ,even on holidays,he takes me to go travelling,we have been to some palaces of interest such as Xian ,Dalian and so on。We enjoyed ourselves very much。

In a word ,i'm proud of having such a good father 。I want him to be both my father and my best friend forever。

问答题


阅读以下关于CAN现场总线嵌入式监控系统的技术说明,根据要求回答问题1至问题5。
[说明]
某自动化仪表企业正在研究使用现场总线网络构成自动监测系统的可行性,打算采用 CAN(Controller Area Network,控制器局域网络)总线作为底层网络构件系统。该企业试验用的数据采集与监测系统的网络结构如图6-10所示。


在图6-10网络结构中,系统主控机可有一台或多台,相当于上位机,负责系统的总体管理,可以向网络节点发送命令,接受节点数据,进行存储、分析、统计、显示与打印等工作。在系统主控机内装有PCCAN网卡(CAN总线通信接口适配卡)。系统主控机中具有以下几种软件模块:
(1)初始化模块。该模块用来设置CAN网络通信速率、输出控制方式、报文标识符屏蔽格式等参数,设定各节点工作空间的位置与规模,初始化节点缓冲区域的缓冲文件等。
(2)采集节点信息与数据模块。该模块可以采用指定节点发送、由节点主动发送和自动轮询采集等多种方式,并可以统计与分析数据采集的进度与状态。
(3)向节点发送参数、命令或程序模块。
(4)数据统计分析模块。
(5)系统管理模块。
图6-10所示的网络结构中有12个网络节点,每一节点都通过传感器采集现场的有关数据。在每一节点电路中都配置了MCP2510 CAN控制器和TJA1050总线收发器,其接口电路如图6-11所示。系统主控机与网络节点采用双绞线连接,实验时最大节点间的距离为35 m。

[问题1]
CAN总线能够使用光纤和(1)等多种传输媒体。总线信号以差分电压传送,两条信号线分别为CAN_H和CAN_L。静态时这两条信号线均为2.5 V,此状态表示(2),也可以称之为“隐性”。CAN_H比CAN_L高,表示逻辑“0”(或称为“显性”),此时,通常电压值为CAN_H=3.5 V,CAN_L=1.5 V。当“显性”位和“隐性”位同时发送时,最后总线数据将为(3)。

判断题