Extend-A-Bus Tutorial
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Tutorial1www.ccontrols.comINTRODUCTION Device level networks such as DeviceNet and Smart DistributedSystem are low-level networks that provide connections betweensimple industrial devices such as sensors and actuators and higher-level devices such as controllers. Benefits of device level networksinclude reduced wiring costs, the ability to exploit the intelligencepresent in some low-level devices and improved diagnosticcapabilities from that of hard-wired systems.ControllerDeviceNetOtherDevicesSensor PushbuttonMotor ClusterStarterAllen-BradleyBar Code ScannerSMCDevice Configuration Input/OutputDevicesMotorControllerFigure 1.Sensors, actuators Driveand controllers canreside on a commonDeviceNet network.Device level networks, in general, generate two types of messages.I/O messages provide all the work by conveying actual real-timedata between controllers and sensors or actuators. This is calledimplicit messaging since a connection is already establishedbetween these devices with an agreed-upon messaging protocol.So there is no need to send protocol information with the data—just the data. This speeds up data transfers.All other messages can be lumped into a class called explicitmessaging. These messages are your traditional source/destinationmessages when protocol information must also be provided inorder to understand what requests or commands are being made.These types of messages are for establishing connections,configuring ports ...
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Controller
DeviceNet
Other Devices SensorPushbutton MotorCluster Starter Allen-Bradley Input/OutputSMCBar Code Scanner Devices Motor Controller Drive
Device Configuration Figure 1. Sensors, actuators and controllers can reside on a common DeviceNet network.
Figure 2. Although DeviceNe and Smart Distribute System incorporat different application layers, they bot incorporate CAN.
ISO Data Link (Layer 2) ISO Physical (Layer 1) ISO Media (Layer 0)
Application Layer
Logical Link Control (LLC) Media Access Control (MAC) Physical Layer Signaling (PLS) Medium Attachment Unit (MAU) Transmission Media
CAN Protocol Specification
Standard Format Arbitration Field S O 11 bit IDENTIFIER F Figure 3. An 11-bit identifier is used in standard format.
Control Data CRC Ack End of Int Bus Field Field Field F. Frame Idle R I r RTDEoDLC0-8 Bytes15 bit CRC
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