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DeviceNet

History
Developed	Layer 1, 2: Bosch AG Layer 7: Rockwell Automation
Norm	IS 11898
User association	ODVA www.odva.org
Market leader	Rockwell Automation/Allen-Bradley
Market	USA, Asia

The CAN protocol was originally developed by Robert BOSCH GmbH for the European automobile industry in order to replace expensive wiring in cars with a cheaper network cable. For an event, the CAN protocol has fast reaction and a high degree of reliability such as is necessary, for example, for controlling the ABS brakes and airbags. From this there has developed a communication standard for application in automation technology.

ControllerAreaNetwork is generally a line network. Every participant hears all messages of the others and can send messages at any time. Simultaneous bus accesses are recognized and released (CSMA/CA) through arbitration within the 11- Bit message header (Identifier). The header thus defines the priority of the message, whereby each can contain up to 8 Bytes of user data.
DeviceNet utilizes the CAN technology for data transmission. The transmission rates in the DeviceNet are 125, 250 and 500 kBaud.
The protocol divides the CAN Identifier into 4 telegram groups and allocates duties to them on the basis of the Client and Server principle.

System data
Max. devices	64
Max. baudrate	500 kBaud
Max. extension	100 m @ 500 kBaud 500 m @ 125 kBaud
Bus access	CSMA/CA
Max. I/O data	unlimited
I/O connection	polled cos cyclic bit-strobed
Communication	Producer / Consumer
Message channel	Explicit unlimited data amount

The procedure is connection-orientated and means that a connection between 2 participants must first be opened in order to then exchange information. For this purpose, each DeviceNet device has either an Unconnected Message Manager (UCMM, for multiple connections or connections without connection Port) or only an Unconnected Port. Both types reserve functions via some of the CAN identifiers depending on the device address. The so-called explicit channel is then opened over this Identifier. Then information is exchanged over this of which I/O connection is to be finally established.

Data of the DeviceNet-Slave Implementation

Connections	Bit Strobe Change of State Cyclic Poll Explicit Peer to Peer Messaging
UCMM	not supported
Fragmentation	Explicit and I/O
Process image	max. 510 bytes
Explicit connection	Get and Set-Attribute Reset services up to 240 bytes per message transferred to the application

Data of the DeviceNet-Master Implementation

Devices	max. 63
Connection	Bit Strobe Change of State Cyclic Poll Explicit Peer to Peer Messaging
UCMM	supported
Fragmentation	Explicit and I/O up to 255 bytes per I/O connection
Explicit Connection	Get and Set-Attribute- Reset services up to 240 byte per message
Process image	max. 7 KByte

Performance DeviceNet Implementation

@ CIF 50-DNM, CIF 30-DNS, 1 MBaud, Polling Mode

Bus cycle time	4,528 ms 8,0697 ms 20,821 ms	@16 Slaves with 2 bytes @16 Slaves with 8 bytes @16 Slaves with 16 bytes
Reaction time	1,92-2,84 ms	@1 Slave with 1 byte