CAN-bus is a bus-based serial communications system used in everything from cars and trucks, through to boats, trains and buildings. It was originally developed for the automotive industry in order to reduce complexity of wiring harnesses on vehicles and to support the increasing amounts of data that today’s machines need in order to operate.
CAN has some distinct advantages that appeal to the off-highway and mobile machine market and Control Technologies UK can work closely with you to help leverage these advantages:
OEMs wishing to adopt CAN-bus can refer to detailed ISO standards that allow common strategies across vehicles. ISO 11898-x is the primary standard for the interchange of digital information for road vehicles and is the cornerstone for the CAN standard. The standard is split into 5 sections:
- ISO 11898-1 (data link layer and physical signalling)
- ISO 11898-2 (high-speed medium access unit)
- ISO 11898-3 (low speed fault-tolerant medium-independent interface)
- ISO 11898-4 (time-triggered CAN)
- ISO 11898-5 (high-speed CAN and low-power applications)
ISO 11898-1 and -2 are the primary documents to be used in the deployment of a CAN application and Control Technologies UK have many years experience working with, and implementing, the standard across a wide range of industries.
As defined in ISO 11898-1, CAN is built to be physically robust, providing excellent protection against electro-magnetic disturbances that can compromise data transmissions. This is done by applying the following principles:
- Twisted cable – CAN is a 2-wire technology (CAN-high and CAN-low) and by using twisted cable, it is possible to neutralise the impact of any disturbance on the differential voltage between CAN-high and CAN-low, which the transceivers use to interpret the data
- Architecture – the standard defines physical parameters for the overall architecture for a CAN system to ensure optimum functionality. These are:
- Overall bus length – dependent on bus speed (baud rate)
- Distance between spurs – CAN operates a ‘straight-line’ architecture (as opposed to a traditional star topology used in IT systems for example)
- Length of spurs
- Shield – it is recommended to shield the CAN cable to further protect against EMI and this shield should only be grounded at 1 end of the cable
- Termination – like all serial communications, CAN uses resistive termination (120Ω resistors) at each end of the bus to ensure stable transmissions and reduce any potential reflections on the bus.
CAN offers significant transmission reliability by use of an efficient error detection mechanism and multi-master functionality to increase the possibility of providing fast recovery from errors, should they occur. CAN also deploys a non-destructive arbitration principle, meaning that when several devices broadcast at the same time, data is not lost, simply delayed until the transmitting node has finished.
As CAN has been adopted across most industries, companies have sought to standardise the CAN protocols used in order to allow isolated development and interconnection. A number of key protocols have been established including the following:
- CAN 2.0B – this is primary protocol that all other protocols are based on.
- SAE J1939 – Managed by the Society of Automotive Engineers, it was designed as the CAN protocol for diesel engine manufacturers. J1939 is widely used across the automotive industry and is being further developed to support electric vehicles.
- CANopen – Managed by CAN in Automation (CiA), CANopen is widely used by sensor manufactures to enable a plug and play level of functionality.
- OSEK/VDX – OSEK (cars)
- DeviceNet – Widely used in industrial automation applications and managed by Rockwell Automation.
It is estimated that there are in excess of 1 billion CAN devices worldwide and this is being added to each year. Virtually every chip manufacturer supports CAN meaning that number manufacturers of electronic controllers, sensors and devices is growing all the time. This leads to a competitive market and reduced cost of implementation.
How can Control Technologies UK help?
We’ve worked with CAN-bus technologies for over 10 years, designing, implementing and delivering solutions to many industries. We know what works and what doesn’t and can support you in various ways, whether it’s adopting CAN for the first time, developing your existing CAN system or generally supporting the system in the field.
If you’d like to find out more about CAN and about how we can work with you, please get in touch today.