Text from page 15 of catalogue Control systems for mobile vehicles
Page 15 of catalogue Control systems for mobile vehicles of ifm Electronic GmbHNotes and explanations
CAN in ecomatmobile components All devices described in this catalogue with CAN interface support the CANopen protocol. When using CANopen devices from ifm electronic configuration can be carried out by means of the programming Software and the control modules (network master) but also by means of external Tools (PC software, CANview analyser). Which tool is best suited depends on the complexity and on the system requirements. ifm electronic supports project engineers and programmers with the appropriate tools and services.
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General information on CANopen The CAN functions described above control the physical link and the data transmission between the bus participants. For a practical CAN application this means that the programmer is responsible for the definition of the data protocol for the specific application. To obtain a uniform protocol for networking different CAN participants CANopen has been defined. It defines the meaning of the data for the corresponding device type (e.g. I /O module, drive, encoder, etc.). With these definitions the application programmer can access many components from different manufacturers with CANopen capability without any intensive work on the protocol. CANopen participants which belong to the same device family have their data organised in the same way. The characteristics of these device classes are indicated in the “device profiles”. Despite this definition the basic CAN structure which allows each bus participant to send messages (data) to the network is maintained. Only the network master (NMT master) exists once and is used, among others, for the initialisation and monitoring of the system. A list of device parameters is defined in CANopen nodes in the object directory (OD) in which all settings are described and stored. It does not only serve as a device description but also as an interface for the access to the data by other CANopen devices. Larger, non time-critical data volumes are transmitted via “Service Data Objects” (SDOs). In addition there are at least two “Process Data Objects” (PDOs) for transmitting and receiving time-critical process data. Monitoring of the participants and the network is also carried out via CAN objects. The “Nodeguarding Object” or the “Heartbeat” monitors if a participant responds within a defined time. “Emergency Objects” are transmitted for the display of hardware and software errors.
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CANopen To make things even simpler for the CAN user the standardised protocol layer CANopen is based on the existing definitions. More and more manufacturers of Machines and installations join to form “user groups” to make their specific definitions on the basis of these standards. This is why CAN with the protocol layer CANopen provides the future-oriented and flexible basis for a bus system in mobile machines and installations.