CAN基础培训-物理层
CAN物理层-CANphysicallayer
CAN物理层-CANphysicallayerCAN物理层-CAN physical layer作者：admin 添加时间：2012-05-05 18:53:30 浏览：474●?位编码●?位定时和同步●?数据速率和总线长度的相关性●?物理介质●?⽹络拓扑●?总线访问●?物理层标准ISO 11898-2 (⾼速)ISO 11898-3 (容错)SAE J2411 (单线)ISO 11992 (点对点)其它控制器局域⽹(CAN)协议在OSI模型(共有七个层)中定义了数据链路层和物理层。
国际标准组织(ISO)定义了包含CAN规范以及部分物理层的标准：物理信令，由位编码和解码(不归零制，简称NRZ)以及位定时和同步组成。
1. 位编码NRZ与曼彻斯特编码法相⽐较在选定的不归零制(NRZ)位编码中，信号电平在位时间内保持恒定，因此仅需要⼀个时间间隙来表⽰位M位编码的其它⽅法例如：曼彻斯特编码法或脉冲宽度调制)。
信号电平可以在较长时段内保持恒定；因此必须采取措施以确保不超过两个信号沿之间的最⼤允许时间间隔。
这对于实现同步⾮常重要。
通过在相等值的五位数后⾯插⼊互补位来应⽤位填充。
当然，接收器不能填⼊填充位，这样才能处理原始数据内容。
2. 位定时和同步在位级(OSI层1，物理层)上，CAN使⽤同步位传输。
这固然加⼤了发送容量，但同时也意味着要求更复杂的位同步⽅法。
⼀旦接收到带有每个字符的起始位，便开始在⾯向字符的传输(⾮同步)中执⾏位同步，这时同步传输协议的帧开头仅有⼀个起始位。
为了能使接收器正确读取消息，需要连续进⾏再同步。
因此请在位时间间隔内，在标称采样点的前后插⼊相位缓冲段。
CAN是可调节的逐位仲裁总线访问协议。
信号从发送到接收应答必须在⼀个位时间内完成。
为了实现同步，传输延迟环节，需要留出传播延迟段。
传播延迟段考虑了总线上的信号传播以及因发送和接收节点⽽导致的信号延迟。
请区分两种类型的同步：帧起始处的硬同步与帧内的再同步。
新能源汽车教学实验系列：CAN总线基本物理层和链路层分析实验及习题思考
文库资料 ©2016 Guangzhou ZHIYUAN Electronics Stock Co., Ltd.
文章源自ZLG 致远电子，转载或引用请注明出处
1 CAN 总线基本物理层和链路层分析实验
一、实验目的
1、熟悉CANScope 软件，掌握CANScope 的操作。
2、利用CANScope 了解基本物理层和链路层的分析方法。
二、实验步骤
1、启动设备，打开控制柜背后柜门，检查CANScope 是否已经接好线，如已接好线，长按CANScope 面板上面的开机按钮进行开机，此时CANScope 闪灯。
在工控机桌面检查软件是否已经安装好， 并且可以正常使用。
2、打开“MotorTest ”、“CANScope ”软件，查看CANScope 是否显示为在线状态。
如果显示“CANScope-离线”则要检查CANScope 驱动是否安装成功或者电源是否打开。
图29.1
CANScope 菜单界面
3、结合广州致远电子股份有限公司的《CANScope 用户手册》的第8.1章节，熟悉CANScope 的基本操作。
三、实验总结和思考
1、自动侦测波特率与自定义波特率有什么作用？
2、实时示波器测量分析有什么作用？
3、眼图分析的方式有什么作用？
4、CAN 报文收发与统计有什么作用？
5、CAN 波形记录与分析有什么作用？
6、CAN 报文重播（录播）有什么作用？
7、FFT 共模干扰频谱分析有什么作用？
8、传输延迟分析与导线等效长度预估有什么作用？
9、波形边沿斜率与带宽分析有什么作用？。
CAN网络基础培训大纲
掌握
CAN总线
CAN 总线概述，简述 CAN 总线的定义、历史、发展等 CAN 总线基本概念，通信模型，相关标准协议，应用特点 CAN 总线物理层，简述总线电平，拓扑结构，外围电路等 CAN总线数据链路层，CAN2.0的基本内容，包括报文收发、 报文帧格式、错误处理机制等
理解 理解 掌握 掌握
CAN总线产品设计基础知识， 简述CAN总线典型电路， 控制器， 理解 收发器选择 基于CAN总线的应用层协议，J1939、CANopen、Devicenet 实操 了解
通过CAN卡互相通信理解CAN总线通信过程，示波器采集CAN波形了解 波形特征
广州虹科电子科技有限公司
CAN 网络基础培训大纲
培训目标 Training Target 了解汽车网络通信整体架构 学习CAN总线基础知识及应用 了解基于CAN的应用层协议 利用CAN卡和示波器采集和分析CAN报文
培训内容 Detailed Content 类别 车辆网络发展趋势 车辆网络架构，简述当前车辆上使用的通信协议类型，网络 的基本架构，了解 CAN 总线在网络中所处的位置 内容 目标 了解
CAN物理层调试基础知识及举例
[导读]控制器局域网（CAN）标准不断发展，正用于车载和工业网络之外的许多新应用。
支持它的微处理器变得普遍且价格低廉，并且开源协议栈让其非常容易访问，同时也容易添加至新系统。
控制器局域网（CAN）标准不断发展，正用于车载和工业网络之外的许多新应用。
支持它的微处理器变得普遍且价格低廉，并且开源协议栈让其非常容易访问，同时也容易添加至新系统。
有许多CAN板可用于BeagleBone （Capes）、Stellaris （BoosterPacks）、Arduino （Shields）和其他微处理器开发平台。
当设计人员的系统上电却不能工作时，应该怎么办呢？本文为您介绍一种对CAN物理层进行调试的较好工程方法。
我们将介绍基础调试步骤，并说明一个CAN物理层应有的性能，以及找出问题的一些小技巧。
调试基础知识ISO11898-2和ISO11898-5规范详细说明了高速CAN物理层即收发器。
掌握CAN物理层的基础知识以后，利用简单的调试工具便可迅速地找出常见问题。
所需的基本实验室工具为示波镜、数字万用表（DMM）和一个电源。
如果想要深入了解问题，则需要更高精度和更复杂的工具。
这种问题已非本文讨论的范畴，但是这里介绍的基础知识可帮助确定问题所属类别，以及进一步调试所需的其他工具。
一个由 TI 组装的CAN演示系统以及TI的SN65NVD255D评估模块（EVM）1，用于演示硬件。
另外，我们还使用了其他一些东西，例如：CAN连接器外接头电缆和芯片钩（抓住收发器引脚，让其连接至电缆，以更加容易地连接示波器指针，如图1所示）。
图1：CAN物理层调试基本工具连接检查开始调试对话时，使用DMM确认印刷电路板（PCB）上连接如我们所预计的那样—系统未上电。
这看似很基础，但令人吃惊的是，这个简单的方法却解决了许多简单问题。
所有人都会认为原理图、布局和制造工艺没有问题，但不幸的是，它们有时却并不如人愿。
子插件板位置错误、虚焊和错误端接或者连接的电缆，都是一些常见问题。
CAN基础培训-物理层
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[3] 比较
高速CAN 应用范围 12V、24V、42V <1 Mbit/s
电压 V 3.5 隐性 显性 隐性
低速容错CAN 12V、24V、42V 40~125 kbit/s
总线电压 拓扑结构 CAN线 电路设计
2.5 1.5 时间
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[4] 收发器选择
低功耗功能
C类：
Clamp-30供电 uC可控制可关闭收发器电源 收发器不具备网络唤醒功能
Clamp-15 A B C D
Vbat
Clamp-30
Vcc
On/Off
Vcc
Ctrl
Vcc
Vcc
Ctrl
uC
Tx Rx
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目录
[1] 高速CAN
应用范围 总线电压 拓扑结构 CAN线 电路设计 CAN线故障的容错性能
[2] 低速容错CAN [3] 比较 [4] 收发器选择
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TRX
uC
Tx Rx
TRX
uC
Tx Rx
TRX
uC
Tx Rx
TRX
CANH CANL 恒润科技公司
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[4] 收发器选择
低功耗功能
D类：
Clamp-15供电 整个ECU由点火开关控制供电
Vbat
Clamp-30 A
can基础知识
概要—CAN特点
(1) 多主控制和仲裁机制 • 在总线空闲时，所有的单元都可开始发送消息（多主控制）。 • 最先访问总线的单元可获得发送权。 • 多个单元同时开始发送时，进行仲裁，优先级高的单元先发送（标识 符=ID=优先级，ID越小，优先级越高）。 (2) 消息的发送 • CAN数据传输类似于“电话会议”。 • 一个电话用户（控制单元）将数据“讲” 入网络中，其他用户通过网络“接听” 这个数据。 • 对这个数据感兴趣的用户就会接收该数 据，而其他用户则选择忽略。 • 在CAN 协议中，所有的消息都以固定的 格式发送。 • 在发送报文过程中进行“回读”，判断 送出的位与回读的位是否一致
• 格式错误：固定格式位场（如CRC界定符、ACK界定符、帧结束等）含 有一个或更多非法位。
数据链路层—帧结构—错误帧
由错误标志和错误界定符构成。
数据链路层—帧结构—错误帧
错误标志：错误标志包括主动错误标志和被动错误标志两种。 • 主动错误标志：6 个位的显性位 • 被动错误标志：6 个位的隐性位 注：错误标志违背“位填充规则”，其他节点也会发送错误标志。故错 误标志在6-12之间。 错误界定符 • 错误界定符由8个位的隐性位构成。 • 节点发送错误标志后，发送隐性位，直至检测到总线上出现隐性位， 之后发送7个剩余隐性位。
• 每个节点都含有REC（接收错误 计数器）和TEC（发送错误计数 器）
• 当接收错误产生时，REC增加； 正确接收到数据帧，REC减少。
• 当发送错误产生时，TEC增加； 正确发送了数据帧，TEC减少。 • REC、TEC的数值会引发节点状 态改变
特例：如果总线上只有一个节点， 该节点发送数据帧后得不到应 答， TEC最大只能计到128，即 节点只会进入被动错误状态而 不会进入总线关闭状态.
CAN总线物理层
CAN Physical LayerThe Controller Area Network (CAN) protocol defines the data link layer and part of the physical layer in the OSI model, which consists of seven layers. The International Standards Organization (ISO) defined a standard, which incorporates the CAN specifications as well as a part of physical layer: the physical signaling, which comprises bit encoding and decoding (Non Return to Zero, NRZ) as well as bit-timing and synchronization.Bit encodingNRZ compared with Manchester bit representationIn the chosen Non Return to Zero (NRZ) bit coding the signal level remains constant over the bit time and thus just one time slot is required for the representation of a bit (other methods of bit encoding are e. g. Manchester or Pulse-width-modulation). The signal level can remain constant over a longer period of time; therefore measures must be taken to ensure that the maximum permissible interval between two signal edges is not exceeded. This is important for synchronization purposes. Bit stuffing is applied by inserting a complementary bit after five bits of equal value. Of course the receiver has to un-stuff the stuff-bits so that the original data content is processed.Bit-timing and synchronizationNominal bit-timeOn the bit-level (OSI layer 1, physical layer) CAN uses synchronous bit transmission. This enhances the transmitting capacity but also means that a sophisticated method of bit synchronization is required. While bit synchronization in a character-oriented transmission (asynchronous) is performed upon the reception of the start bit available with each character, a synchronous transmission protocol there is just one start bit available at the beginning of a frame. To enable the receiver to correctly read the messages, continuous resynchronization is required. Phase buffer segments are therefore inserted before and after the nominal sample point within a bit interval.The CAN protocol regulates bus access by bit-wise arbitration. The signal propagation from sender to receiver and back to the sender must be completed within one bit-time. For synchronization purposes a further time segment, the propagation delay segment, is needed in addition to the time reserved for synchronization, the phase buffer segments. The propagation delay segment takes into account the signal propagation on the bus as well as signal delays caused by transmitting and receiving nodes.Two types of synchronization are distinguished: hard synchronization at the start of a frame and resynchronization within a frame.•After a hard synchronization the bit time is restarted at the end of the sync segment. Therefore the edge, which caused the hard synchronization, lies within the sync segment of the restarted bit time.•Resynchronization shortens or lengthens the bit time so that the sample point is shifted according to the detected edgeThe device designer may program the bit-timing parameters in the CAN controller by means of the appropriate registers.Interdependency of data rate and bus lengthDepending on the size of the propagation delay segment the maximum possible bus length at a specific data rate (or the maximum possible data rate at a specific bus length) can be determined. The signal propagation is determined by the two nodes within the system that are farthest apart from each other. It is the time that it takes a signal to travel from one node to the one farthest apart (taking into account the delay caused by the transmitting and receiving node), synchronization and the signal from the second node to travel back to the first one. Only then can the first node decide whether its own signal level (recessive in this case) is the actual level on the bus or whether it has been replaced by the dominant level by another node. This fact is important for bus arbitration.Some modern transceivers support no low data rates. Therefore on acquisition of transceivers the maximal required network length must be considered.Physical mediaThis clause is most interesting for system designers.The basis for transmitting CAN messages and for competing for bus access is the ability to represent a dominant and a recessive bit value. This is possible for electrical and optical media so far. Also powerline and wireless transmission is possible.For electrical media the differential output bus voltages are defined in ISO 11898-2 and ISO 11898-3, in SAE J2411, and ISO 11992 (see below).With optical media the recessive level is represented by "dark" and the dominant level by "light".The physical media most commonly used to implement CAN networks is a differentially driven pair of wired with common return. For vehicle body electronics single wire bus lines are also used. Some efforts have been made to develop a solution for the transmission of CAN signals on the same line as the power supply.The parameters of the electrical medium become important when the bus length is increased. Signal propagation, the line resistance and wire cross sections are factors when dimensioning a network. In order to achieve the highest possible bit rate at a given length, a high signal speed is required. For long bus lines thevoltage drops over the length of the bus line. The wire cross section necessary is calculated by the permissible voltage drop of the signal level between the two nodes farthest apart in the system and the overall input resistance of all connected receivers. The permissible voltage drop must be such that the signal level can be reliably interpreted at any receiving node.The consideration of electromagnetic compatibility and choice of cables and connectors belongs also to the tasks of a system integrator.assumed line length 100 mSpecific signal propagation time (ns/m)Maximum bit rate (kbit/s)5.0805.5736.0676.5627.058Network topologyThis clause is most interesting for system designers.Electrical signals on the bus are reflected at the ends of the electrical line unless measures against that have been taken. For the node to read the bus level correctly it is important that signal reflections are avoided. This is done by terminating the bus line with a termination resistor at both ends of the bus and by avoiding unnecessarily long stubs lines of the bus. The highest possible product of transmission rate and bus length line is achieved by keeping as close as possible to a single line structure and by terminating both ends of the line. Specific recommendations for this can be found in the according standards (i.e. ISO 11898-2 and -3).It is possible to overcome the limitations of the basic line topology by using repeaters, bridges or gateways. A repeater transfers an electrical signal from one physical bus segment to another segment. The signal is only refreshed and the repeater can be regarded as a passive component comparable to a cable. The repeater divides a bus into two physically independent segments. This causes an additional signal propagation time. However, it is logically just one bus system.A bridge connects two logically separated networks on the data link layer (OSIlayer 2). This is so that the CAN identifiers are unique in each of the two bus systems. Bridges implement a storage function and can forward messages or parts thereof in an independent time-delayed transmission. Bridges differ from repeaters since they forward messages, which are not local, while repeaters forward all electrical signals including the CAN identifier.A gateway provides the connection of networks with different higher-layer protocols. It therefore performs the translation of protocol data between two communication systems. This translation takes place on the application layer (OSI layer 7).Bus accessThe connection between a CAN controller chip and a two-wire differential bus a variety of CAN transceiver chips according to different physical layer standards are available (see below ISO 11898-2 and -3, etc.).This interface basically consists of a transmitting amplifier and a receiving amplifier (transceiver = transmit and receive). Aside from the adaptation of the signal representation between chip and bus medium the transceiver has to meet a series of additional requirements. As a transmitter it provides sufficient driver output capacity and protects the on-controller-chip driver against overloading. It also reduces electromagnetic radiation. As a receiver the CAN transceiver provides a defined recessive signal level and protects the on-controller-chip input comparator against over-voltages on the bus lines. It also extends the common mode range of the input comparator in the CAN controller and provides sufficient input sensitivity. Furthermore it detects bus errors such as line breakage, short circuits, shorts to ground, etc. A further function of the transceiver can also be the galvanic isolation of a CAN node and the bus line.Physical layer standardsISO 11898-2 high speedISO 11898-2 is the most used physical layer standard for CAN networks. It describes the bus access unit (implemented as CAN high-speed transceiver) functions as well as some medium-dependent interface features.In this standard the data rate is defined up to 1 Mbit/s with a theoretically possible bus length of 40 m at 1 Mbit/s. The high-speed standard specifies a two-wire differential bus whereby the number of nodes is limited by the electrical busload. The characteristic line impedance is 120 Ohm, the common mode voltage ranges from -2 V on CAN_L to +7 V on CAN_H. The nominal specific propagation delay of the two-wire bus line is specified at 5 ns/m. All these figures are valid only for a 1 Mbit/s transfer rate and a maximum network length of 40 m.In order to achieve physical compatibility all nodes in the network must use the same or a similar bit-timing. For automotive applications the SAE published the SAE J2284 specification. For industrial and other non-automotive applications the system designer may use the CiA 102 recommendation. This specification defines the bit-timing for rates of 10 kbit/s to 1 Mbit/s. It also provides recommendations for bus lines and for connectors and pin assignment.ISO 11898-3 fault-tolerantAn alternative form of bus interfacing and arrangement of bus lines is specified in ISO 11898-3 (fault-tolerant CAN). This standard is mainly used for body electronics in the automotive industry. Since for this specification a short network was assumed, the problem of signal reflection is not as important as for long bus lines. This makes the use of an open bus line possible.This means low bus drivers can be used for networks with very low power consumption and the bus topology is no longer limited to a linear structure. It is possible to transmit data asymmetrically over just one bus line in case of an electrical failure of one of the bus lines.ISO 11898-3 defines data rates up to 125 kbit/s with the maximum bus length depending on the data rate used and the busload. Up to 32 nodes per network are specified. The common mode voltage ranges between -2 V and +7 V. The power supply is defined at 5 V.Transceiver chips, which support this standard, are available from several companies. The fault-tolerant transceivers support the complete error management including the detection of bus errors and automatic switching to asymmetrical signal transmission.SAE J2411 single wireThe single-wire standard SAE J2411 is also for CAN network applications with low requirements regarding bit rate and bus length. The communication takes place via just one bus line with a nominal data rate of 33,3 kbit/s (83,3 kbit/s in high-speed mode for diagnostics). The standard defines up to 32 nodes per network. The main application area of this standard is in comfort electronics networks in motor vehicles.An unshielded single wire is defined as the bus medium. A linear bus topology structure is not necessary. The standard includes selective node sleep capability, which allows regular communication to take place among several nodes while others are left in a sleep state. Transceivers for this standard are available, too.ISO 11992 point-to-pointAn additional approach to using CAN low-speed networks with fault-tolerant functionality is specified in the ISO 11992 standard. It defines a point-to-point connection for use in e.g. towing vehicles and their trailers. For one vehicle with one trailer, a point-to-point connection is defined. For one vehicle with two trailers, a daisy-chain connection is defined. The nominal data rate is 125 kbit/s with a maximum bus line length of 40 m. The standard defines the bus error management and the supply voltage (12 V or 24 V). An unshielded twisted pair of wires is defined as the bus medium.OthersNot standardized are fiber-optical transmissions of CAN signals. Due to the directed coupling into the optical media, the transmitting and receiving lines must be provided separately. Also, each receiving line must be externally coupled with each transmitting line in order to ensure bit monitoring. A star coupler can implement this. The use of a passive star coupler is possible with a small number of nodes, thus this kind of network is limited in size. The extension of a CAN network with optical media is limited by the light power, the power attenuation along the line and the star coupler rather than the signal propagation as in electrical lines.Advantages of optical media are emission- and immission-free transmission andcomplete galvanic decoupling. The electrically neutral behavior is important for applications in explosive or electromagnetically disturbed environments.CAN总线物理层控制局域网（CAN）协议决定数据链路层和在OSI模式中部分物理层。
CAN总线(一)物理层-屏蔽双绞线
1、物理层一般要求1．1 物理层物理层实现网络中电控单元（ECU）的电连接。
ECU 的数目限制于总线线路的负载承受能力。
根据本部分的电气参数定义，在特定网段上ECU 的最大数目定为30。
1．2 物理介质物理介质为屏蔽双绞线。
双绞线特性阻抗为120Ω，电流对称驱动。
两条线分别命名为CAN_H 和CAN_L。
相应ECU 的管脚引线也分别用CAN_H 和CAN_L 来表示。
第三条连接屏蔽终端的线用CAN_SHLD 表示。
1．3 差动电压CAN_H和CAN_L相对于每个单独ECU地的电压有VCAN_H和VCAN_L 。
VCAN_H和VCAN_L间的差动电压由下式计算：Vdiff = VCAN_H — VCAN_L1．4 总线电平总线总是处于两种逻辑状态，即隐性和显性的其中之一（见图1）。
在隐性状态VCAN_H和VCAN_L 固定在一个中值电压电平。
在带终端电阻的总线上，Vdiff 接近于零。
显性状态由大于最小门限的差动电压表示。
显性状态覆盖隐性状态并在显性位中传输。
1．5 仲裁期间的总线电平在特定的位时间里，总线线路上两个不同的ECU 的显性位和隐性位的冲突仲裁结果是显性位。
（见图1）1．6 共模的总线电压范围共模的总线电压范围定义为CAN_H 和CAN_L 的边界电压值。
在连接在总线上的所有ECU 正常运行的前提下，CAN_H 和CAN_L 的电压值由各个ECU 对地测得。
1．7 总线终端在线路的两个末端上，必须接有负载电阻R 终结L。
RL 不得放置在ECU 中，以避免其中一个ECU 断线，总线将失去终端（见图2）。
1．8 内部电阻ECU 的内部电阻Rin 为隐性位状态，ECU 和总线线路断开下的CAN_H（或CAN_L）和ECU 地之间的电阻值。
（见图3）。
1．9 差动内部电阻ECU 的差动内部电阻Rdiff 为隐性位状态，ECU 和总线线路断开下的CAN_H 和CAN_L间的电阻值。
（见图4）。
1．10 内部电容ECU 的内部电容Cin 为隐性位状态，ECU 和总线线路断开下的CAN_H（或CAN_L）和ECU 逻辑地之间的电容值。
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CAN总线技术基础培训
概述及物理层
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主要内容
概述
CAN的发展概况 CAN的性能特点 CAN的协议标准
CAN物理层
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概述
车辆总线的发展概况
CAN的发展概况
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概述
CAN的性能特点
保证系统数据一致性
接口的抗电磁干扰能力设计 每帧信息都采用CRC校验及其他检错措施，错误漏检率极低 错误报文的自动重发、临时错误的恢复以及严重错误的自动 关闭，保证不影响其它节点的通信
节点A 应用层
报文
节点n
…
错误检测 错误处理
报文
…
数据链路层
比特流
物理层
差分电压
传输速率最高可达1Mbps，距离最远可达10km 通信介质选择灵活（双绞线、同轴电缆、光纤） 采用双线差分信号 协议本身对节点的数量没有限制 总线上节点的数量可以动态改变，组网灵活 短帧结构，传输时间短，受干扰概率低
节点A 应用层
报文
节点n
位速率/kbps 1000 500
…
报文
…
200 100 50 20
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总结
概述
CAN的发展概况 CAN的性能特点 CAN的协议标准 CAN节点结构 CAN收发器 总线电压 CAN传输介质 拓扑结构 CAN线故障的容错性能 CAN总线连接器
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CAN基础培训－概述及物理层
RL CAN_H CAN_L
(1) CAN_H开路 (2) CAN_L开路 (3) CAN_H对VBAT短路 (4) CAN_L对GND短路 (5) CAN_H对GND短路 (6) CAN_L对VBAT短路 (7) CAN_H对CAN_L短路 (8) CAN_H和CAN_L开路 (9) 终端电阻开路
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CAN物理层
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符合ISO11898-2标准，最高速率1Mbps； 抗环境瞬间干扰，具有保护总线能力； 斜率控制，降低射频干扰RFI； 热保护以及电源和地短路保护； 未上电的节点对总线无影响； 低电流待机模式；
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Body Control Powertrain Control
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Transmission
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Dash
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电压(V)
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~ 1.5 V
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车载网络的要求
采用串行总线拓扑结构 节点可以动态改变 具有极好的抗干扰能力 极强的差错检测和处理能力 满足信息传输实时性要求 具备故障的诊断和处理能力 考虑到成本因素，要求其控制接口结构简单，易 于配置
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概述
1983年，Bosch开始研究用于汽车的串行总线系统 1986年，Bosch在SAE大会上首次公布CAN协议 1987年，Intel推出了第一片CAN控制器芯片 1991年，Bosch颁布CAN 2.0技术规范 1991年，CAN最先在Benz S系列轿车上实现 1993年，ISO颁布CAN的国际标准 ISO-11898 CAN 被广泛的用于各类自动化控制领域
CAN_H
40m@1Mbps CAN_L
EMI
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CAN的发展概况 CAN的性能特点 CAN的协议标准
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CAN的协议标准
OSI参考模型
协议层的相互作用
OSI参考模型 7 应用层 6 表示层 5 会话层 4 传输层 3 网络层 2 数据链路层 1 物理层 OSI参考模型 7 应用层 6 表示层 5 会话层 4 传输层 3 网络层 2 数据链路层 1 物理层
车辆总线的发展概况
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位速率 /kbps ~10 应用场合 车身系统 应用范围 电动门窗、座椅调节、灯光照 明控制等 电子仪表、驾驶信息、故障诊 断、安全气囊、自动空调等
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10~125
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125~1000
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主要内容
概述 CAN物理层(基于ISO11898-2)
CAN节点结构 CAN收发器 总线电压 CAN传输介质 拓扑结构 CAN线故障的容错性能 CAN总线连接器
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总线电压
隐性 1 0 0 0 1 0 1 0 0
电压 V 3.5
1 0
总线物理信号
逻辑信号
显性
隐性
显性
隐性
CAN_H
若总线上有两个以上驱动 器同时分别发送“0”和 “1”，其结果是总线数值 为显性“0”
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CAN的协议标准
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...........
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终端 电阻 D L
l
终端 电阻
网络拓扑参数
参数 总线长度 支线长度 节点距离 终端电阻 符号 L l D RL 单位 m m m 欧 数值
最小
0 0 0.1 100
名义
最大
40 0.3 40
条件 波特率为1Mbps
任意波特率
120
130
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CAN物理层
CAN线故障的容错性能
双绞线
屏蔽双绞线 非屏蔽双绞线
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双绞线参数 参数 特征阻抗 单位电阻 单位延迟 符号 Z R 单位 Ω mΩ/m ns/m 数值 最小 95 名义 120 70 5 最大 140
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CAN物理层
拓扑结构
ECU 1
ECU 2
ECU n
总线型拓扑
CAN 节点1 case7 case5 case6 Vbat CAN 节点n-1 case3 Vbat case1 CAN 节点n case9 RL case4 GND case2 case8 GND
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CAN物理层
CAN总线连接器
OBD连接器引脚定义
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