CANopen Characteristics 33003798.00 Feb_2006
Contents Abbreviations...3 Introduction...4 Performance...5 High Fault Tolerance...5 High Flexibility...6 High Data Throughput...7 Detailed Diagnostic Options...8 Installation...9 Constraints...10 Costs...12 Cabling...12 Additional Network Components...12 Size...13 Cable Length...13 Repeaters...14 Other Prevailing Factors...14 Contact...15 Introduction This document is intended to provide a quick introduction to the described bus system. It is not intended to replace any specific product documentation. On the contrary, it offers additional information to the product documentation, for installing, configuring and starting up the bus system. CANopen Characteristics_EN.doc Schneider Electric 2
Abbreviations Word/Expression AC Advantys Altivar CANopen CB ConneXium DC EDS E-OFF Harmony HMI I/O IclA (ICLA) Lexium/Lexium05 Magelis MB - SL Micro NIM PC Phaseo PLC Powersuite Premium Preventa PS SE Sycon Telefast Tesys U Twido TwidoSoft Unity (Pro) Vijeo Designer VSD WxHxD XBT-L1000 Meaning Alternating Current SE product name for a family of I/O modules SE product name for a family of VSDs Name for a communications machine bus system Circuit Breaker SE product name for a Family of Transparent Factory devices Direct Current Electronic Data Sheet Emergency Off switch SE product name for a family of switches and indicators Human Machine Interface Input/Output SE product name for a compact drive SE product name for a family of servo-drives SE product name for a family of HMI-Devices SE name for a serial Modbus communications protocol SE product name for a middle range family of PLCs SE product name for a Network Interface Module Personal Computer SE product name for a family of power supplies Programmable Logic Computer An SE software product for configuring ALTIVAR drives SE product name for a middle range family of PLCs SE product name for a family of safety devices Power Supply Schneider Electric SE product name of a Field bus programming software SE product name for a series of distributed I/O devices SE product name for a decentralized I/O System (Small Terminal Block) SE product name of a middle range family of PLCs SE product name for a PLC programming software SE product name for a PLC programming software An SE software product for programming Magelis HMI devices Variable Speed Drive Dimensions : Width, Height and Depth An SE software product for programming Magelis HMI devices CANopen Characteristics_EN.doc Schneider Electric 3
Introduction In Schneider Electric s network strategy, at field level, CANopen ranks as the core network for machines and installations. The aim of this document is to outline the strengths and weaknesses of CANopen for machines and installations using the catalog of criteria known as PICCS. The acronym PICCS stands for: P = Performance I = Installation C = Constraints C = Costs S = Size CANopen Characteristics_EN.doc Schneider Electric 4
Performance Introduction On the basis of performance, CANopen is the ideal bus for machines and installations. Its specific advantages are: High fault tolerance High flexibility High data throughput Detailed diagnostic options High Fault Tolerance Reliable EMC CANopen data is transmitted using differential signal transmission. Moreover, the common is routed in the bus cable. The combination of these two features means that CANopen has excellent EMC characteristics. Optimum error detection Hamming distance indicates the probability of an error occurring during data transmission but not being detected by the checking mechanisms in place on the bus. The following principle applies: the greater the hamming distance, the lower the probability. The hamming distance of CANopen is 6 (by way of comparison, the hamming distance on fieldbuses is usually 4). This means that on average, on the basis of: a baud rate of 500 kbps a bus load of 20% and 2000 operating hours per year a transmission error will go undetected once every 1000 years. CANopen Characteristics_EN.doc Schneider Electric 5
High Flexibility The data on a CANopen device can be distributed across a number of PDOs flexibly in accordance with update requirements. Special bus parameters can be used to optimize PDO transmission frequency, priority levels and synchronization. Selected devices are also able to communicate directly with one another. This means that communication can be tailored to suit the specific needs of each individual application. The following parameters are used for this purpose: COB-ID Transmission Type (possibly with Inhibit Time and Event Timer) COB-ID If a number of devices wish to transmit data at the same time, the COB-ID will define a clear transmission sequence. The rule: the lower the COB-ID, the higher the priority. Direct communication relationships between individual devices (direct data exchange) can be set up by assigning COB-IDs accordingly. Transmission Type The Transmission Type parameter defines the transmission frequency of an individual PDO. PDOs can be transmitted synchronously (on the basis of a unique global network SYNC command), cyclically or when data changes. This means that the transmission characteristics of PDOs can be adapted specifically to the data to be sent, for example: Synchronous for drives Cyclic for analog values On changes for digital values CANopen Knowledge The level of knowledge required will vary. Users who wish to benefit from higher levels of flexibility will need a more in-depth knowledge of CANopen. However, as users are not always in possession of the requisite knowledge and default settings are perfectly adequate in many cases, Schneider has classified its devices into the following conformance classes: M10, M20, M30 for masters and S10, S20, S30 for slaves. The higher a device's classification, the more extensive its optimization options and features. However, the level of knowledge of CANopen required also increases accordingly. CANopen Characteristics_EN.doc Schneider Electric 6
High Data Throughput The very low overhead in the CAN telegram and the provider consumer model mean that CANopen is optimized for high data throughput. Moreover, potential collisions can be detected in advance and are, therefore, very rare. Examples The two examples below are designed to illustrate data throughput (1 Mbit transmission rate): Transmission time for 256 digital I/O points: < 1 ms Transmission time for 128 analog I/O words: < 5 ms Data volume Up to 508 PDO per direction can be configured for a CANopen network. In a maximum configuration of this type, all identifiers reserved for PDOs will be used. These 508 PDOs can be distributed across up to 126 nodes. If this technique is used, an average of 4 PDOs per direction will be available per node, equating to a maximum data volume of 32 bytes per direction. However, in theory, all PDOs can be mapped on a single "mammoth" device. In reality, the maximum value is limited both by the CANopen device itself and by the CANopen master. On the CPP1100, this limit value is 64 PDOs per CANopen device. This means that with 32 PDOs per direction, a device of this type can, for example, transmit up to 256 bytes of input data and 256 bytes of output data (by way of comparison, Profibus is able to transmit 244 bytes per device). However, using just 16 slaves of this type will use up all identifiers reserved for PDOs. The Schneider Electric conformance classes referred to above give rise to the following minimum values in respect of the total number of PDOs to be supported: M10: 64 PDOs M20: 252 PDOs M30: 504 PDOs CANopen Characteristics_EN.doc Schneider Electric 7
Detailed Diagnostic Options Error control CANopen has two different error control mechanisms, node guarding and heartbeat. Both of these enable the application to manage what are known as life lists providing information about the communication state of the individual devices. Schneider Electric has declared the heartbeat mechanism binding for its devices, due to its being more effective in communication and supporting, to a certain degree, intra-device monitoring. Emergency Each CANopen device can use the emergency mechanism to communicate a change in its internal state, e.g., the failure of I/O channels or a following error on drives. Emergency telegrams can be evaluated in the application, thereby making it possible to respond to specific events in I/O peripherals. CANopen Object Dictionary The CANopen object dictionary contains the following objects, which provide the user with advanced options for diagnosing and identifying the devices on a bus. These objects can be read out via SDOs and made available to the application. Examples: Object Meaning 1000 Device Type 1001 Error Register 1003 Predefined Error Field 1018 Identity Object Finally, all objects in the object dictionary associated with one device can be read out. This provides a means of obtaining a comprehensive overview of the configuration of a device as well as of the states of all inputs and outputs - in other words, diagnostics in its truest sense. CANopen Characteristics_EN.doc Schneider Electric 8
Installation Topology The structure of a CANopen network can be designed in accordance with a variety of topologies. Users may choose between: Looping through the line (as on Profibus) Setting up spur lines (as on Modbus Plus) and local stars Combining the two structures In this way, CANopen networks can be optimized in accordance with the spatial conditions prevailing in a system. Considerable savings can be made in respect of the amount of cable used. Degree of protection CANopen devices are available with both IP20 and IP67 protection. Preassembled cables in a variety of lengths and fitted with corresponding connectors enable direct installation of devices locally without having to rely on installation cabinets. Installation Equipment Schneider Electric is able to offer its customers all the installation equipment they will need for efficient and cost-saving assembly from a single supplier. They can either choose preassembled cables (from our extensive range) or cut cables and fit them with connectors themselves. Our range of cables includes: CANopen cables in a variety of lengths and certified for either the American or European market Cables suitable for trailing are also available CANopen connectors with disconnectable terminating resistors and 90 o or 180 o cable outlets Connectors with diagnostic interface are also available TAPs for setting up local stars, with RJ45 or DSUB interface Preassembled cables in a variety of lengths and fitted with various connectors (DSUB, RJ45, M12 circular connectors) CANopen Characteristics_EN.doc Schneider Electric 9
Constraints General This section deals with the restrictions of CANopen. Like all other bus systems, CANopen has its limits and there are areas of application for which other bus systems are more suitable. A detailed examination of the following points affecting machines and installations shows that they are relatively insignificant and, therefore, do not adversely affect the overall profile of CANopen. Cable Length The maximum cable length supported by CANopen while maintaining efficient transmission rates is 250 m (250 kbps). Although longer cables can be used (e.g., 500 m at 125 kbps), the reduced baud rate means that there will also be a loss in bandwidth during transmission, and this cannot always be supported by machines and installations. Although longer cables are typically required in process automation, they are an exception where machines and installations are concerned. Cables can be extended using bridges to support exceptions of this type. Repeaters, which are common on other fieldbuses (e.g., Profibus) are not suitable for this purpose. User-Data Length The maximum user-data length in a CAN telegram is limited to 8 bytes. Compared with a Profibus telegram, which is able to transmit up to 244 bytes, this seems to be a serious disadvantage. However, please bear the following points in mind: Smaller message packets can be transmitted much more quickly and with less overhead. As well as being able to distribute their user data across a number of nodes, CANopen nodes are able to assign priorities in respect of the communication process and transmit at various frequencies. On machines and installations, it is more common for larger volumes of data to have to be transferred at data distribution level (control level) than at data acquisition level (machine bus). Longer telegrams (as on Profibus, for example) are much more susceptible to electromagnetic interference. This means that what at first sight seems to be a disadvantage can actually transpire to be an advantage in respect of flexibility. User-Data Volume On CANopen, user-data volume is restricted to a maximum of 508 PDOs in each transmission direction. A PDO length of 8 bytes results in a maximum of 4064 bytes for inputs and 4064 bytes for outputs. If we consider that even the preferred implementation ("distributed CANopen") has fewer than 2000 input and output bytes, the CANopen userdata volume is entirely adequate for machines and installations. CANopen Characteristics_EN.doc Schneider Electric 10
Conformance Classes By classifying its devices as outlined above, Schneider Electric has created a scale for device complexity. The devices within a class are matched in terms of performance. Less complex devices require less knowledge of CANopen. Many settings are predefined and cannot be changed. However, this does restrict optimization options and device performance. More complex devices are capable of higher levels of performance and their communication characteristics can be optimized. However, they do require significantly more advanced knowledge of CANopen on the part of the user. Users can now identify the relevant class and focus their requirements accordingly. An extract from the conformance classes appears in the tables below. Examples for masters M10 M20 M30 (minimum Slave ID 1... 16 1... 63 1... 127 requirement) Baud rate [kbps] 125, 250. 500 M10 + 50, 1000 M20 + 10, 20, 800 Number of devices 16 63 126 COB ID Read-only Read/Write Read/Write Transmission Type 254, 255 M10 + 0, 1-240 As M20 Number of PDOs 64 252 504 SYNC No Producer Consumer/producer EMY Consumer Consumer/producer As M20 Heartbeat 16 consumers, 63 consumers, 126 consumers, 1 producer 1 producer 1 producer Node guarding No Yes Yes Examples for Slaves S10 S20 S30 (minimum Slave ID 1... 63 1... 127 1... 127 requirement) Baud rate [kbps] 125, 250. 500 S10 + 50, 1000 S20 + 10, 20, 800 COB ID Read-only Read/Write Read/Write Transmission Type 254, 255 S10 + 0, 1-240 As S20 PDO mapping Fixed Fixed Configurable SYNC - Consumer Consumer/producer EMY Producer Producer Consumer/producer Heartbeat 1 consumer, As S10 As S20 1 producer Node guarding No Yes Yes CANopen Characteristics_EN.doc Schneider Electric 11
Costs General Installation costs (both for equipment and personnel) are a central criterion when selecting a network. Choosing and installing CANopen costs approximately 20% less than other fieldbuses. Cabling Looping Through the Bus Cable CANopen supports what is known as the looping through of the bus cable. Here, the incoming and outgoing cables are bridged in the connector and the connection to the device itself is established via a short spur. This makes structural components vital to other types of network such as Ethernet (hubs, switches) superfluous. Even TAPs are not required (although they can and in some cases should be used). Connectors For components with IP20 protection, screw-type 9-pin SUBD connectors are used as standard. This enables cables to be tailored to meet the precise requirements of a machine with standard tools. Special tools such as pliers are not required. Users wishing to use preassembled cables to minimize connector assembly time can do so. For components with IP67 protection, preassembled cables in a variety of lengths fitted with M12 circular connectors are available. Additional Network Components Large Network Segments Possible While on other fieldbuses with more than 32 nodes repeaters are required, which means that additional costs are incurred the more nodes are used, CANopen segments can operate with up to 64 nodes. It is only above this number that repeaters or bridges are required. This means that repeaters simply do not figure in the majority of applications. CANopen as a Generic Interface Many devices, such as variable speed drives or servo drives, feature a CANopen interface as standard. This means that users do not need to purchase special interface cards for the fieldbus connection, as is generally the case, for example, for Profibus or INTERBUS. When we consider that it is precisely servo drives and variable speed drives whose use is widespread in applications involving machines and installations, this proves a significant advantage in terms of cost. CANopen Characteristics_EN.doc Schneider Electric 12
Size Cable Length Maximum Cable Length The spatial dimensions of a machine are limited primarily by the permissible cable lengths supported by the communication network. The table below illustrates the relationship between cable length and bit rate for the CANopen cable types offered by Schneider Electric. Bit rate [kbps] 1000 800 500 250 125 50 20 10 Max. length [m] 20 40 100 250 500 1000 2500 5000 Note A maximum cable length of 40 m for 1 Mbit is frequently quoted in CANopen documentation. This value applies to networks, which do not feature isolation between bus interface and device, something that is standard on Schneider products. On networks with isolation, the calculated maximum value is 4 m. However, experience in the field has shown a practical length to be 20 m, although this does have to be reduced if spur lines are used and/or subject to other factors prevailing. Maximum Spur Length Spur lines (or spurs) are permitted on CANopen networks. They are linked to the main cable via TAPs. The values indicated in the table below apply to individual spurs and minimum TAP distance. Bit rate [kbps] 1000 800 500 250 125 50 20 10 Individual spur [m] 0.3 3 5 5 5 60 150 300 Total per TAP [m] 0.6 6 10 10 10 120 300 600 Min. TAP distance* 3.6 6 6 6 72 180 360 Grand total [m] 1.5 15 30 60 120 300 750 1500 * Can be calculated individually for each TAP: Min. TAP distance = 60% of total of all spurs in the TAP CANopen Characteristics_EN.doc Schneider Electric 13
Repeaters Repeaters (or bridges) have to be used on networks with 64 or more devices. Repeaters delay the propagation of the bus signal on the cable, thereby reducing the permissible cable length. Delaying propagation time by 5 ns will reduce cable length by 1 m. A repeater with a delay of, e.g., 5 ns, will reduce the maximum cable length by 30 m. Other Prevailing Factors The definitions in the conformance classes - such as the number of devices supported, for example - also affect the possible size of a machine or installation in terms of both spatial dimensions and data volume. Please see the tables in the "Constraints" section for more information. CANopen Characteristics_EN.doc Schneider Electric 14
Contact Author Telephone E-Mail Schneider Electric GmbH Customer & Market System & Architecture Architecture Definition Support +49 6182 81 2555 cm.systems@de.schneider-electric.com Schneider Electric GmbH Steinheimer Strasse 117 D - 63500 Seligenstadt Germany CANopen Characteristics_EN.doc As standards, specifications and designs change from time to time, please ask for confirmation of the information given in this publication. 15