CAL (CAN Application Layer) and CANopen J. Novák Czech Technical University in Prague Faculty of Electrical Engineering Department of Measurement

CAN based Industrial Distributed System

n ISO at physical (high-speed) and link layers n Proprietary application layer protocol –Difficult replacement of nodes by product of other manufacturer –Requires changes in other node programs –Very low flexibility –High costs of ownership

CANopen Standard Structure n ISO (high-speed) at physical and link layers n CAL at application layer n Communication, application profiles and device profiles at user layer

CAL – CAN Application Layer n Set of application layer protocols –CMS – CAN Message Specification defines and controls access to variables, events and domains –NMT – Network Management implements node addressing controls the network start-up –DBT – Distributor provides dynamic identifier distribution –LMT – Layer Management physical layer addressing, assigning of NMT addresses physical layer parameters setting

CAL – basic mechanisms

CMS – CAN Message Specification n Defines three basic object types –variables, events, domains n Objects are defined by attributes –name, priority, data type, access rights and so on n Variables –process data transfer among nodes –basic or multiplexed multiplexer is an index n Events –support the information transfer about asynchronous events may carry concrete value n Domains –transfer of unstructured data –basic or multiplexed

NMT – Network Management

n Provides services and protocols for –network parameterization –network start-up –network management –error detection and reporting n Master – Slave structure n Nodes addressing by NMT address (NodeID) –range 0 – 255, 0 = broadcast –assigned by LMT service or proprietary –uses identifier 0

NMT – Network Management Reset Application Reset Communication Init Pre-operational Disconnected Connecting Preparing Operational Prepared 02 3 CAL Initialization

DBT and LMT – Distributor and Layer Management n Distributor provides possibility of dynamic identifiers assignment within the network start-up –Master – Slave structure –not often used alternative methods of identifiers assignment are used instead n LMT provides NMT address assignment based on the physical (LMT) node address, physical layer parameter setting –Master – Slave structure again –not often used alternative methods of NMT address assignment alternative methods of bit rate setting

CANopen – Node Structure n Object Directory –Data structure, containing definition of all objects describing both the application and communication behavior of particular node –Communication and application are parameterized by data from the directory –Communication is defined by the communication profile, application by application profiles or by device profiles

Object Directory

SDO – Service Data Object n Object Directory Access Protocols –protocol for multiplexed domains is used –index and subindex are parameters –object access rights depend on concrete object and also on the node state (NMT management) read only when network is running –application and communication objects can be initialized before the network starts –SDO communication has low priority – high frame identifiers

PDO – Process Data Object n Protocols for process data transfer –protocol for stored events is used –each PDO is defined by 2 objects in directory PDO Communication parameters PDO Mapping –communication parameters define ID, transmission type, inhibit time –mapping defines up to 64 fields, that are transferred by single PDO mapping is dynamic at the network start-up by SDO communication –PDO communication has higher priority

Predefined communication objects n Defined by communication profile –Sync Provides the synchronization of selected object transmission Protocol of CMS variable Write only

Predefined communication objects n Defined by communication profile –Timestamp Allows the time distribution For highly accurate synchronization the High Resolution Synchronization Protocol is available –Emergency Allows information about errors in application part of module standard error codes are defined

Device Profiles, Network Configuration n Unification of functions and implementation of devices with similar features –allows to replace device of one manufacturer by the product of other manufacturer without application SW changes, if they share common profile n Network configuration is supported by EDS (Electronic Data Sheet) files –contain the template of object directory can be easily imported into the configuration systems and concrete content of object directories of concrete nodes is derived from them