CANH
CANL
D=101
R=101
Recessive RecessiveDominant
1 10
V
CANH
V
CANL
1 1-bit
Identifier
R
T
R
I
D
E
r 0
D L C
0 …8
C R C
A C K
r 1
1 8-bit
Identifier
S
R
R
S
O
F
BytesData
E
O
F
E
O
F
E
O
F
F
I
S
A CAN Message
www.ti.com
4
SLOA101B–August 2002–Revised May 2016
Submit Documentation Feedback
Copyright © 2002–2016, Texas Instruments Incorporated
Introduction to the Controller Area Network (CAN)
3.1.2 Extended CAN
Figure 3. Extended CAN: 29-Bit Identifier
As shown in Figure 3, the Extended CAN message is the same as the Standard message with the
addition of:
• SRR–The substitute remote request (SRR) bit replaces the RTR bit in the standard message location
as a placeholder in the extended format.
• IDE–A recessive bit in the identifier extension (IDE) indicates that more identifier bits follow. The 18-bit
extension follows IDE.
• r1–Following the RTR and r0 bits, an additional reserve bit has been included ahead of the DLC bit.
4 A CAN Message
4.1 Arbitration
A fundamental CAN characteristic shown in Figure 4 is the opposite logic state between the bus, and the
driver input and receiver output. Normally, a logic-high is associated with a one, and a logic-low is
associated with a zero - but not so on a CAN bus. This is why TI CAN transceivers have the driver input
and receiver output pins passively pulled high internally, so that in the absence of any input, the device
automatically defaults to a recessive bus state on all input and output pins.
Figure 4. The Inverted Logic of a CAN Bus
Bus access is event-driven and takes place randomly. If two nodes try to occupy the bus simultaneously,
access is implemented with a nondestructive, bit-wise arbitration. Nondestructive means that the node
winning arbitration just continues on with the message, without the message being destroyed or corrupted
by another node.
The allocation of priority to messages in the identifier is a feature of CAN that makes it particularly
attractive for use within a real-time control environment. The lower the binary message identifier number,
the higher its priority. An identifier consisting entirely of zeros is the highest priority message on a network
because it holds the bus dominant the longest. Therefore, if two nodes begin to transmit simultaneously,
the node that sends a last identifier bit as a zero (dominant) while the other nodes send a one (recessive)
retains control of the CAN bus and goes on to complete its message. A dominant bit always overwrites a
recessive bit on a CAN bus.
剩余16页未读，继续阅读
duangq
- 粉丝: 1
- 资源: 13
我的内容管理
收起
- 我的资源
快来上传第一个资源
我的收益 登录查看自己的收益
我的积分
登录查看自己的积分
我的C币
登录后查看C币余额
我的收藏 
我的下载 
下载帮助
会员权益专享
最新资源
- 利用迪杰斯特拉算法的全国交通咨询系统设计与实现
- 全国交通咨询系统C++实现源码解析
- DFT与FFT应用：信号频谱分析实验
- MATLAB图论算法实现：最小费用最大流
- MATLAB常用命令完全指南
- 共创智慧灯杆数据运营公司——抢占5G市场
- 中山农情统计分析系统项目实施与管理策略
- XX省中小学智慧校园建设实施方案
- 中山农情统计分析系统项目实施方案
- MATLAB函数详解：从Text到Size的实用指南
- 考虑速度与加速度限制的工业机器人轨迹规划与实时补偿算法
- Matlab进行统计回归分析：从单因素到双因素方差分析
- 智慧灯杆数据运营公司策划书：抢占5G市场，打造智慧城市新载体
- Photoshop基础与色彩知识：信息时代的PS认证考试全攻略
- Photoshop技能测试：核心概念与操作
- Photoshop试题与答案详解
资源上传下载、课程学习等过程中有任何疑问或建议，欢迎提出宝贵意见哦~我们会及时处理！
点击此处反馈
