Which bus, when?

It's now easier to see which kind of industrial bus best serves particular industries and applications. Connectors from Lumberg Inc., Midlothian, Va., are tailored for industrial Ethernet. The hybrid design combines an RJ45 electrical connection with the common M12/M18 shell, and protects against moisture buildup, dust, corrosion, EMI/RFI, vibration, and shock. Snap Ultimate I/O from Opto 22, Temecula, Calif., supports 10 and 100 Mbits/sec Ethernet, as well as Modbus/TCP, XML, SMTP, and FireWire. It handles I/O, networking, and provides connectivity to other levels of the business. Few topics in industry have been as vigorously debated as industrial networking. The so-called fieldbus wars raged throughout the 1990s with as many as two dozen contenders. After all is said and done, five industrial networks are now widely deployed throughout the world. They are, in no particular order, DeviceNet, Ethernet, Foundation Fieldbus, Modbus, and Profibus. Several networks have had varying degrees of success. SDS from Honeywell competed with DeviceNet, but never gained wide acceptance. Interbus from Phoenix Contact has done well in Europe. And ASInterface has found a limited niche of smaller applications that require just digital I/O. In many respects, the fieldbus debates mirror the old Beta versus VHS conflict; the formats that prevailed are not necessarily technically superior. In the end, the success of a network depends on broad industry support and successful marketing. No surprise that the most successful networks are backed by large companies: Siemens with Profibus, Rockwell with DeviceNet, Schneider with Modbus, and Fisher-Rosemount with Foundation Fieldbus. Industrial Ethernet is somewhat of an exception, but the specific application protocols are still backed by large companies. Profibus is the world's most widely used industrial network. Recognized by its characteristic purple cable and based on RS-485, it is associated with Siemens and is dominant in Europe and South America. Although recent revisions to the protocol have added configuration, diagnostic, and peer-to-peer capabilities, the most widely deployed version is simple Profibus DP that employs polled master/slave I/O. On the downside, the high