20 years of CiA 401: Perhaps the most implemented CANopen profile

CiA 401, the CANopen device profile for generic I/O modules, was released in 1996 and has been consistently used by manufacturers. Future plans for CiA 401 include mapping for 64-byte process data objects (PDOs) and enhancing interoperability, with discussions underway about safety and security.

By Holger Zeltwanger, CAN in Automation April 6, 2016

The CAN in Automation (CiA) 401 profile specification was developed by the Esprit project developing the CAL-based communication profile. After handing over to CiA for further development and maintenance, the profile for modular input/output (I/O) devices was released internally as version 1.3 in 1996 and implemented by several companies. In those times, CiA members edited the specifications. Today, CiA engineers do it. Developments continue to enhance interoperability, and discussions are looking at safety and security.

The CiA profile supports different digital I/O granularities. Besides the mandatory 8-bit digital process data, 16-bit or 32-bit access was specified as well as a bit-wise access. For analog I/Os, the profile provides 16-bit resolution (mandatory) as well as 32-bit, floating point, and manufacturer-specific data types. 

Process data objects

Version 1.4 pre-defined just two process data objects (PDOs). Version 2.0 used already pre-defined PDOs. The first PDO-transmitted digital inputs respectively received digital outputs. The other three PDOs contained four analog I/O values. In case of other I/O port capability, the devices need to be configured. To avoid this, CiA 401 version 3.0 introduced the "M"-bit in the device type object (index 1000h), which indicates that a manufacturer-specific PDO mapping is implemented.

Since version 3.1, the profile is split into two parts. Part 1 specifies generic I/O modules; part 2 describes several joystick implementations with dedicated PDO mappings and some specific parameters. There is also the CiA 852 recommended practice for CiA 401-based operator environment sub-systems developed for construction and mining machines. However, the recommendation has not been implemented very often. In fact, the CiA 401 generic profile is one of the most used and implemented I/O specifications. In particular, the second part of CiA 401 has been improved and specifies additional joystick PDO mappings.

There are many modular CANopen I/O devices on the market, and there are more CiA 401 implementations. Some of these implementations such as I/O devices in IP65-rated enclosures are very specific. Many of the CANopen suppliers for construction machines and off-road vehicles provide I/O modules compliant to CiA 401. There are also micro-controllers with pre-programmed CiA 401 compliant software available. These I/O chips are designed to simplify the device design of CANopen I/O modules. 

The future of CiA 401

Although CiA 401 is 20 years old, there are some new enhancements under development. The PDO mapping is going to be updated due to the longer data frames (up to 64-byte) provided by the CAN FD data link layer. There is also demand to improve the interoperability between host controllers and CiA 401 modules, which could be achieved by device classes using dedicated mappings specified in CiA 852. Another option is combining analog and digital I/O data in pre-defined PDOs, which hasn’t been done in the past. CiA members are also discussing adding functional safety and security features in the longer PDOs.

Holger Zeltwanger is managing director, CAN in Automation (CiA). CAN in Automation is a CFE Media content partner. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.


Key Concepts

The CiA 401 profile for modular input/output (I/O) devices was released internally as version 1.3 in 1996 and implemented by several companies. 

There are many modular CANopen I/O devices on the market, and there are more CiA 401 implementations designed for specific applications such as micro-controllers.

Future plans for CiA 401 include updating the PDO mapping to accommodate 64-byte data frames provided by the CAN FD data link layer.

Consider this

What other updates should be added to CiA 401 and what benefits could they provide?

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