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

Computer Networks and Securitydevice should receive the frame. Along with the identifier, other piecesof information are added to the frame, such as data length, data bytes,error checking, and frame acknowledgment.One type of CAN network is called a producer/consumer network.This type of network allows any device to produce or send amessage to any other device. This can be done without any interactionfrom a host or master. This type of network decreases the amount of bustraffic.When a device transmits a message onto the CAN bus network, allother network devices receive that message. Each receiving device conductsa test on the incoming frame identifier to determine if the messageis intended for that device.When transmitting, a device examines the network to ensure thathigher-priority identifiers have precedence using a collision-handlingsystem called non-destructive bitwise arbitration.The CAN bus provides a physical layer that is implementedthrough CAN controllers and transceivers. It is a multidrop networkwith no limitation on the number of devices, provided that the electricalcharacteristics of the signal remains within specifications. The CAN buscable carries both the power and signal.The CAN bus defines the hardware requirements and how dataframes are transported using a communication medium. A higher-levelprotocol (HLP) is needed for communications management to set therules, behavior, and format of the data frames. HLPs for CAN bus technologyinclude DeviceNet, CANopen, Smart Distributed Systems, CANApplication Layer (CAL), and CAN Kingdom.CANopenCANopen is a set of specifications with a communication profile aswell as device, interface, and application profiles. The communicationprofile is based on the CAN data-link layer and the high-speed physicallayer specified in ISO 11898. CANopen was initially developed in theESPRIT/ASPIC project by Bosch. In 1994, CANopen was transferred tothe CAN in Automation (CIA) international users and manufacturersgroup based in Germany. CANopen has been used as an open networkin production lines, power plants, robot control, medical equipment,military systems, and building automation.©2001 by The Fairmont Press, Inc. All rights reserved.