Embedded Networking with CANopen

By Olaf Pfeiffer

When it comes to Embedded Networking, Embedded Internetworking seems to be a trend and the only topic around these days. Although the idea of having all our embedded devices accessible via the Internet is tempting, for many embedded applications, Internet access does not solve the real communication requirements often set within the device.

First published in Circuit Cellar, September 2001

[ Select a Protocol | HLP | Overview | Device Profiles | EDS | PDO | NMT | Implementing ]

Selecting a Communication Protocol

The requirements for more internal communication come from another trend: adding more intelligence to many machines, appliances and other devices. The side effect of this trend is, that more communication between I/O points or distributed control systems is required. For machine internal communication, TCP/IP is usually a complete overkill, especially if the embedded controllers are on the low end of the performance scale. More cost efficient solutions are serial protocols. Standard serial interfaces like UARTs, I2C or CAN are available on-chip with many microcontrollers in the 8-bit and 16-bit arena, allowing for an easy connection of several nodes.

One of the problems with implementing Embedded Networking solutions based on these serial protocols is, that by themselves they do not have a standardized application layer specifying how the data exchanged is structured and how or when it is exchanged. They usually just cover the Physical and Data Link Layers of the standard communication reference model.

That leaves anybody implementing an Embedded Network with these protocols most likely ending up with a proprietary solution. An internal communication specification has to be generated and most likely all the network nodes are built in-house. Outsourcing is difficult, due to the lack of available communication standards. Without higher layer communication standards it is not easily possible for third parties to build efficient off-the-shelf plug-and-play components.

However, the availability of off-the-shelf components for Embedded Internetworking becomes presently more and more important. In all industries we do feel the constant pressure to further shorten the development time and to cut the development costs.

Instead of developing all components from scratch a manufacturer of any machine could choose off-the-shelf sensors and actuators with a standardized networking interface, allowing the development focus to be on system integration and development of the components that bring the companies true IP into the product.

From all the on-chip communication interfaces available with many microcontrollers these days, CAN is the one that gets us closest to the scenario outlined above. Existing standards based around CAN allow for the availability of off-the-shelf components like generic analog and digital I/O devices and can still provide the network designer with enough freedom to optimize the overall system to best meet the communication requirements of a specific application.

[ Select a Protocol | HLP | Overview | Device Profiles | EDS | PDO | NMT | Implementing ]

Copyright © 2001 Circuit Cellar. All rights reserved.

ESAcademy, 2000

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