如何选择和开发DeviceNet系统

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.本文来自织梦 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,本文来自织梦 Allen-Bradley turned DeviceNet over to ODVA, Open DeviceNet Vendors Association.

基于DeviceNet的网络架构