DeviceNet® Communications

What is DeviceNet?

DeviceNet is a cost-effective communications link designed to replace hardwired I/O interconnection between industrial devices. Offering advantages over other industrial networking protocols in the following areas.

Simplicity

Through the use of automated software configuration tools and simple wiring layouts, engineering cost and time to design, configure and commission a DeviceNet installation is significantly less than other comparable networks. Easy adaptation and reuse of previous system designs enables further design efficiencies are achieved.

Device interchangeability

Common definition of simple devices allows interchangeability while making interconnectivity of more complex devices possible. In addition to reading the state of discrete devices, DeviceNet allows easy access to operating node variables such as process temperatures, alarm status as well as system diagnostic status.

Open standard

The specification and protocol are open. This has led to a rapid proliferation of DeviceNet compatible control and instrumentation equipment from a wide range of vendors.

Reliable communication

The DeviceNet communication link is based on a broadcast-oriented, communications protocol the Controller Area Network (CAN). The CAN protocol was originally developed by BOSCH for the automotive market, replacing expensive automatic wire harnesses. As a result, the CAN protocol has fast response and has been demonstrated to be highly reliable in demanding safety critical vehicle applications.

Summary of DeviceNet features and functionality

Network size Up to 64 nodes
Network length

Selectable end-to-end network distance varies with speed

Baud rate Distance
125 kbps 500m
250 kbps 250m
500 kbps 100m
Data packets Variable length, 0-8 bytes
Bus topology Linear (trunkline/dropline)
Media Media 1 twisted-pair for power, for signal in a single shielded cable
Bus addressing

1. Peer-to-peer with Multi-Cast (one-to-many);

2. Multi-Master

3. Master/Slave special case; polled or change-of-state (exception-based)

System features Removal and replacement of devices from the network under power

DeviceNet physical layer and media

The basic trunkline-dropline topology provides separate twisted pair busses for both signal and power distribution. Thick or thin cable can be used for either trunklines or droplines. End to end network distance varies with data rate and cable size.

Figure 1 basic trunkline-dropline topology

Nodes can be removed or inserted from the network without powering down the network.

DeviceNet network cable/data rate limits

Data rates 125Kbps 250Kbps 500Kbps
Thick trunk length 500m 250m 100m
Thin trunk length 100m 100m 100m
Maximum drop length 6m 6m 6m
Cumulative drop length 156m 78m 39m

Maximum end-to-end network distance with data rate and cable thickness.

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