Industrial Ethernet: Bottom to top, 1Gb CC-Link IE connects them all

Nagoya, Japan —The

,IE and the standard version of CC-Link (originally developed by

) is that the new version uses the increasingly popular Ethernet physical layer, rather than RS-485. [See also

]

Ethernet is a worldwide standard for management / IT networking, having essentially displaced all other data-communication methods. At the production-network level, however, a number of standards are in wide use. European control engineers most commonly specify Profibus or its Ethernet version Profinet, which were originally developed by European automation giant Siemens. In North America, DeviceNet holds the largest share, according to CLPA general manager Stephen Jones. (DeviceNet was originally developed by Rockwell Automation, which similarly turned it over to a governing organization.)

With the announcement of CC-Link IE, all three standards now have versions running on Ethernet physical layer. “CC-Link IE, however, is the only one specifically developed to use Gigabit Ethernet over optical fiber,” Jones asserts. Gigabit Ethernet (gigE) is the only network fast enough to assure effective real-time machine control, he continues. Optical fiber provides plenty of bandwidth to carry gigE signals while providing additional benefits, such as immunity to electromagnetic interference (EMI) and reduced weight relative to copper wire Cat-5 Ethernet cabling.

One of CC-Link IE’s most significant features is its self-healing ability. Despite the fact that most current Ethernet installations use star-network topology, the physical standard was originally intended as a multi-drop backbone and can work with other topologies as well. CC-Link IE specifically uses bi-directional token ring topology, with one node acting as a control station for the entire network. In the event that one of the ring segments suffers an electrical failure (such as, short or open), the ring’s bidirectionality allows the control station to maintain communication with all of the nodes at essentially undiminished speed. Similarly, a node failure does not interfere with communication between the remaining nodes.

The system is even robust against multiple network failures. Generally, two failures are enough to separate the ring into two isolated segments, making it impossible for the control station to communicate with the nodes isolated on the other segment. A third failure would break it into three parts, etc. CC-Link IE makes provision to keep nodes on those isolated segments running.

Every node has a MAC address and, in the event that a group of nodes loses communication with the control station, the node on the isolated segment having the lowest MAC address takes over as a sub-control station. By having all stations retain copies of the latest 256 kB token, the sub-control station has all the information needed to keep the nodes remaining in its segment operating.

The CC-Link IE specification is available for download from the CLPA website . The first CC-Link IE products are expected to become available during the first quarter of 2008. CLPA expects to announce additional specifications for CC-Link IE field network and motion network standards later in 2008, and a CC-Link IE safety network standard in 2009.

— C.G. Masi, senior editor
Control Engineering
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