In the case of the CAN (controller area network) serial bus data link, a non-standard has now become a standard in fact, according to Holger Zeltwanger, managing director of CAN in Automation (CiA, www.can-cia.de), an international trade association that provides technical and marketing information, and fosters future developments. He notes that more than 50 off-the-shelf microcontrollers from over 15 chipmakers have the CAN option built in (see caption for the latest). "If it is on all of these, then it is in effect a standard for implementing a reliable data link," he notes.
"The data bus has widespread use in both U.S. and European-made cars—300 million chips this year alone in European cars (at 30 chips per car)," says Zeltwanger. And non-automotive applications in Europe are about five years ahead of the U.S., he offers. Europeans have put CAN in systems from commercial coffee brewing machines to elevators, trucks, trains, and aircraft. CAN is embedded more by machine builders in Europe, whereas in the U.S. the focus has been on communications for factory automation. "And most CAN applications don't push the speed limit," Zeltwanger adds. While its maximum data rate of 1 Mbit/sec is needed for rapid, precise pick-and-place and automotive control tasks, most uses only require 250-500 kbit/sec.
Zeltwanger views CAN today as analogous to having alphabet characters that must be formed into languages users agree on. He notes, "It needs standard integration of higher level protocols." But that said, all that users need are standard "phrases" (profiles) to get along in writing applications, much like international travelers use to make themselves understood, rather than be concerned with the complete rules of grammar. He adds that, because they are so large, automakers have specified their own languages and the CANopen language for automation was developed by users.
CAN Extended: Improved CAN flexibility
and greater memory are keys to the latest PICmicro flash microcontrollers
from Microchip Technology (www.microchip.com). Their scalable
ECAN interface module has three software-configurable operating modes:
legacy for compatibility with existing microcontrollers; enhanced with
additional functions; and FIFO for sequential message storage. The single
module enables multiple applications to be configured on a single node.
Product Manager Greg Robinson says easier, hardware-based CAN use allows
shorter development time. He adds the high voltage of hte chips' physical
layer and higher bus voltage boost noise immunity for applications, such
as controlling motors near high-voltage devices in medical equipment.
On the application level, users and organizations are trying agree on interfaces between protocols, as is now the case with CAN and higher speed, up to 400 Mbit/sec, FireWire. Then, for example, a profile to control hydraulics would just need its parameters changed to function with different bus protocols. "In the future we won't talk buses but profiles," Zeltwanger says. He also notes other cooperative efforts now underway, such as that headed by the U.S. National Institute of Standards and Technology (NIST, www.nist.gov) defining standards for sensors in non-automotive applications.