DeviceNet networks generally adopt a Controller-Device Architecture, wherein a controller device (like a PLC) orchestrates communication with multiple devices, including sensors, actuators, and drives. The controller device is responsible for initiating communication, sending commands, requesting data, and managing network traffic to optimize network performance. The protocol's communication architecture is built upon several core principles and features, each playing a vital role in ensuring efficient and reliable data exchange:
Physical Layer
It leverages the robust Controller Area Network (CAN) bus technology. This layer consists of components such as cables, nodes, taps, and termination resistors, forming a trunkline-dropline topology and is responsible for setting the electrical characteristics and signaling specifications necessary for device interactions. The CAN bus is particularly adept at facilitating dependable communication across extended distances in industrial environments, utilizing twisted pair wiring to maintain signal integrity.
Data Link Layer
The data link layer employs the Controller Area Network (CAN) standard, which manages messaging between controllers and devices. For the network and transport layers, DeviceNet establishes connections using unique identifiers for each node, allowing for up to 64 possible connections. The functions include message framing, error detection, and arbitration, all of which contribute to the deterministic and trustworthy communication that DeviceNet is known for. The ISO 11898-1 standard forms the backbone of this layer, providing a solid foundation for data link operations.
Application Layer
Is where the exchange of data and commands between networked devices is defined. It outlines the structure of messages, addressing schemes, prioritization rules, and error management procedures. Central to this layer is the Common Industrial Protocol (CIP), which offers a uniform framework for device communication within industrial automation systems.
Object Dictionary
The Object Dictionary defines the supported data objects and parameters for each network device, ensuring a standardized interface for accessing device data and functionality. This promotes coherent information sharing, ESD Support and seamless device integration. Typically articulated in the Electronic Data Sheet (EDS) format, it outlines the attributes and properties of each data object.
EDS files
Electronic Data Sheet (EDS) files are simple text files containing information about devices that assist in commissioning them onto the network. These files describe component characteristics so that components can communicate and be recognized on a network.
Furthermore, DeviceNet's messaging system encompasses explicit, implicit, and I/O messaging, each tailored to specific communication needs
Explicit messaging
operates on a command-response model, where structured commands are sent from one device to another, requesting specific actions or data. These commands include a service code that identifies the requested service, and the message may contain additional data required to execute the service. Upon receipt of a command, the target device processes it, executes the requested action, and sends back a response message, which acknowledges the command and may include the requested data or status information.
Implicit messaging
designed for real-time data exchange, where data packets containing time-critical information such as sensor readings or equipment status are transmitted periodically without explicit commands. This type of messaging is essential for applications requiring deterministic communication, where the timing of message delivery is crucial.
I/O messaging
facilitates synchronous data transfer between devices. It involves the exchange of input and output signals in a coordinated manner, with precise timing to ensure reliable and deterministic data transfer for control loops. This ensures minimal latency and effective coordination of input and output operations.
DeviceNet network topologies offer a range of configurations to suit various industrial automation needs. One common topology is the bus topology with branching arrangement, which connects devices through smaller lines branching off from a main line. This topology allows for the addition or removal of devices without needing to power down the system. DeviceNet also supports flexible wiring options such as star type connections using branching taps. These configurations contribute to the overall adaptability of the network's physical layout.
