问答系列（六）-专业自动化论坛-中国工控网论坛

问答系列（六）点击：1739 | 回复：0

精华：1099帖
求助：0帖
帖子：14392帖 | 54470回
年度积分：0
历史总积分：622
注册：2008年9月08日

发表于：2002-10-15 09:19:00

楼主

Are there any plans to use CAN 2.0B (extended) with DeviceNet? Answered by Nick Jones, System Architecture SIG, e-mail: A126) CAN 2.0B extends the 11-bit identifier defined by CAN 2.0A to 29 bits. DeviceNet uses the 11-bit identifier field defined by CAN2.0A, allocating 2,032 message identifiers available into four groups. Groups 1, 2 and 3 are further divided into sub-groups assigned to the 64 MAC IDs. This scheme assigns a limited number of message identifiers to each MAC ID. There have been no discussions at the System Architecture SIG to date about possible use of the 29-bit extended CAN identifier frames (CAN 2.0B). Use of the extra 18 bits would increase the number of unique message identifiers available to each MAC ID by a factor of 262,144. The downside is that the existence of extended frames on the network adds to network overhead and reduces determinism by increasing the potential jitter in a given message transmission. The System Architecture SIG would have to have a clearly defined market requirement that cannot be satisfied with the current protocol to develop an extension of DeviceNet that used the 29-bit identifier frame. The SIG wants to avoid building additional complexity into DeviceNet without a clear reason to do so. Q163) Bus Comparisons. See also Physical Layer (PL)
What is difference between the DeviceNet physical layer and what is commonly referred to as CiA physical layer (ISO 11898 plus 9-pin subD connector per CiA definition)? Answered by Viktor Schiffer, email: A163) DeviceNet is based on ISO 11898. This means it meets (or exceeds) the ISO requirements. Since DeviceNet is designed for up to 64 nodes on the network while ISO 11898 only makes provision for 32 nodes, DeviceNet requires a special CAN transceiver. The specifications for this transceiver are defined in the DeviceNet Specifcation (Volume I, Appendix A). Philips 82C250 is an integrated transceiver that meets the DeviceNet Specification. DeviceNet requires a miswiring and ground interruption protection circuit. Details of this circuit are described in the DeviceNet Specification (Volume I, chapter 9.2.2). DeviceNet only supports three baud rates: 125, 250 and 500 Kbaud (whereas CAN is specified for data transfer rates from 40 baud up to 1 Mbaud). The 1 Mbaud rate is not included in DeviceNet because it is difficult to design opto-isolated nodes running at 1 Mbaud. DeviceNet defines three styles of connectors - Phoenix Combicon open style connectors and two sealed connectors for use in harsh environments. Further details can be found in the DeviceNet Specification (Volume I, Chapter 9.3.5 and Appendix C ). The 9-pin subD connector as defined by CiA is not allowed for DeviceNet products. DeviceNet has a 24 VDC supply voltage carried in the bus cable. The bus transceiver circuitry must be powered from this voltage. Two types of bus cables (thick and thin style) have been specified for DeviceNet. DeviceNet systems may work with other cables, but there is no guarantee that these systems can be operated up to the physical layer limits given in the specification. Q164) Bus Comparisons. See also Physical Layer (PL)
A similar question... We have an existing I/O Block using CAN. Can we just change a software driver and use the same hardware to implement DeviceNet? Answered by Ronald Holl, System Architecture SIG, email: A164) All hardware can be reused except the physical layer interface. You will need to add optical isolation for miswiring protection and DeviceNet connectors (no 9-pin subD connectors). Also, new communication code will need to be added.

分享到：

邀请回答

回复楼主

热门招聘

﻿问答系列（六） ﻿点击：1739 | 回复：0

问答系列（六）点击：1739 | 回复：0