HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumStandardizedCAN NetworkingIn the early years of CAN, each CAN-based embedded networkhad its own protocol. CANopen deals with the CAN-specific detailssuch as bit timing and implementation. It provides standardized communicationobjects (COBs) for real-time data, configuration data andnetwork management data.Besides standardizing communication objects, CANopen specifiesthe description of application objects. The CANopen device profilesdefine application objects for the basic interoperability of CANopendevices. To test this interoperability, there is a CANopen conformancetest tool. CIA uses this tool for certifying CANopen devices.In CANopen, the communication objects for decentralized controlapplications are standardized and described in an object dictionary. Theobject dictionary allows CANopen to distinguish more than 2,048 objects.Communication ObjectsProcess data objects are mapped to a single CAN frame using all8 bytes of the data. Each object has an identifier and may be transmittedby only one node, but it can receive from more than one.Service data objects transmit configuration data, which may belonger than 8 bytes. The transport protocol allows the transmission ofobjects of any size.Network management objects consist of the boot-up object, networkmanagement object, and error-control object. The boot-up objecthas the same identifier as the error control object and is transmittedafter initialization before the node is set into a preoperational state.The network management object is the highest priority object in aCANopen network and is transmitted by the network managementmaster node.Sync, emergency indication and time-stamp transmission objectsare broadcast periodically by the sync producer. The sync object providesthe network clock. Emergency objects are triggered by a devicefatal error and are transmitted from an emergency client on the applicationdevice.©2001 by The Fairmont Press, Inc. All rights reserved.