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□ 简介
什么是DeviceNet?
DeviceNet构建于CAN总线的基础之上，使用CAN总线11位标识区，只使用标准帧。11位标识区中，5位用于表示报文类型(32种报文)，另外6位表示总线地址(64个地址)。
DeviceNet是一个简单的网络化解决方案，降低了成本及安装设备和配线的时间，并提供良好的互换性，使得多家供货商的产品可以像组件一样可以互换。DeviceNet是一个开放的网络标准。其规范和协议都是开放的。供货商不必购买硬件，软件，或许可权限，就可以把设备接入一个DeviceNet系统。其规范文本可以从Open DeviceNet Vendor Association Inc.( ODVA)获得。
DeviceNet在达成众多复杂设备之间的互操作性的同时，也允许简单设备之间的互换性。DeviceNet通讯连接基于广播的通讯协议，即CAN协议。1996年，CAN芯片的出货量超过10million片。主要的一些CAN芯片的供货商有Intel, Motorola, Phillips and Hitachi.
DeviceNet的出现有两个目的：
** 传送与现场级设备相关的控制信息.
** 传送其它与系统控制间接相关的信息，比如配置信息(Configuration).
□ DeviceNet的特点
下表列出了DeviceNet主要的物理媒介层特性:
总线类型 CSMA/BA, master-to-slave, explicit and solicited messaging. Unsolicited messaging, multiple masters, and peer-to-peer was introduced in early 1996 by the Systems SIG group of the ODVA for approval, conformance review and implementation in 1996 and 1997.
节点总数 64
总线拓扑 带分支线的线性网络
通讯距离 500 meters full trunk line, 6 meter branches @ 125 kbps
250 meters full trunk line, 6 meter branches @ 250 kbps
100 meters full trunk line, 6 meter branches @ 500 kbps
156 meters accumulative distance of the branches @ 125 kbps
78 meters accumulative distance of the branches @ 250 kbps
39 meters accumulative distance of the branches @ 500 kbps
传输媒介 Full trunk line - 2 wire twisted shielded cable with 2 wire bus power
cable and drain wire.Thin trunk line - same as full above but with lesser wire size which is more economical and easier to install.
传输信号 Square wave digital with NRZ (Non Return to Zero) encoding
输入点数 64 bits (allocated in bytes) standard in polling mode, larger fragmented messages are supported.
输出点数 64 bits (allocated in bytes) standard in polling mode 24 bits in explicit messaging. Fragmented messages are also supported.
通讯速率 125 kbps, 250 kbps, 500 kbps
总线电源 8 Amp full trunk line, 4 Amp thin line
重复地址侦测 Yes, nodes announce address on start-up and all listen. If a duplicate address is heard, the duplicate node will not advance to run mode.
从站检测 Yes, a list is programmed in the interface and checked
错误侦测 Yes, CRC
错误纠正 Yes, nodes that detect errors signal the sender to repeat.
地址设定
Off line via hand held programmer or with a dedicated interface and host.
On line via the interface master using a reserved newcomer default address that is changed to an application address. Dip/rotary switches are optional.
节点参数编程 Can be very extensive to include drive/rotational and instrument parameters
历史 The early days of DeviceNet were essentially Allen-Bradley. In 1992, Allen-Bradley started to share information and invite not only strategic partners, but direct competitors to become DeviceNet members. DeviceNet was released at the ICEE show in Chicago, March 1994. Then, a year later,
Allen-Bradley turned DeviceNet over to ODVA, Open DeviceNet Vendors Association.
摘要:
DeviceNet拥有所有成功的因素：芯片技术，强大的发起者(Allen-Bradley)，通过开发平台，网络管理软件就可以达成，另外还有一个强大的供货商群体(ODVA)来改善，提高和发展其产品.
□ DeviceNet带来的好处
提高设计的弹性
·通过提供网络数据流的能力来提供无限制的IO端口
·提供互操作性和即插即用能力
改善的过程数据管理
·提供对等(Peer-to-Peer)或主/从(Master/Slave)管理
·作为一个快速响应处理元的结果，提高了吞吐量和可重复性
-包含在位置刻度和预先事件及报警通知中的隐含诊断信息
-在诊断中可延长定期检修的间隔周期
·降低安装成本
- 简化配线，避免了潜在的错误点，减少了所需的文件，减少劳动力资源并节省了安装空间
□ 基于DeviceNet的网络架构