Controller Area Network
The Controller Area Network was one of the first in-card technologies developed in the 80s by BOSCH and first introduced in model year 1992. It remains the most widely used solution for connecting Engine Control Units (ECU).
The Key Benefits for Automotive are:
- Cost effective
- Robust, even in harsh environments
- Long term availability
- Weight saving over non-networked implementations
- Built-in message priority scheme
- Built-in error recovery mechanism
Arasan has a long history of providing IP Solutions to Tier 1 and Tier 2 automotive suppliers. Arasan has added CAN Total IP Solutions to meet the advanced automotive requirements. Our offering includes:
- CAN 2.0
- CAN FD
- CAN Transceiver
Arasan provides Total IP Solutions for a wide range of applications from mobile and mobile-influenced ecosystem that now includes advanced automotive electronics. Arasan recently introduced Reliability Proven One Time-Step Gigabit Ethernet 1588 with AVB for timing sensitive networks in automobiles. Arasan also provides storage controllers for SD and eMMC, and camera and display interface controllers to the automotive industry.
The bus topology uses shared two level connections (CAN_Hi and CAN_Lo). ECUs are connected across a termination impedance. The messaging protocol is Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) with arbitration based on an ECU’s priority level (defined in advance). Packets are 8 bytes and multiple packet messages are allowed.
HS CAN support 1Mbps and LS CAN supports 125kbps. The new CAN FD standard supports rates greater than 1Mbps.CAN uses NRZ Non Return to Zero endcoding. The change from 1 to 0 is immediate but the change from 0 to 1 is dependent on the discharge rate governed by the number of terminations and stub impedances in the network. Typically this means the HS CAN can only effectively achieve 500kbps.
CAN for Avionics
CAN is also used in avionics with adaptions for ARINC 825 standards. The ARINC 825 standard was driven by Airbus and Boeing and defines a communication standard for airborne systems using CAN. It is supported Developed by the CAN Technical Working Group of the Airlines Electronic Engineering Committee (AEEC) with members included Airbus, Boeing, Rockwell Collins, GE Aviation, Vector Informatik.
First application was on A318 and A340 for cabin ventilation system control. CAN is now deployed in a range of applications such as environmental control system, fire detection, door controller, water & waste, oxygen systems, galley, seat actuation, cargo loading systems.
The motivation for CAN FD is more ECUs, more nodes, more networks, more data. CAN FD shares the physical layer, with the CAN protocol as defined in the BOSCH CAN Specification 2.0. ? CAN FD is a serial communications protocol based on CAN 2.0.
New features added:
- Support dual bit rates within a message
- Arbitration-Phase – same bit rate as standard CAN
- Data-Phase – bit rates higher 1 Mbit/s are possible (up to ~5 Mbit/s)
- Support larger data lengths than “classic” CAN
- System cost similar to standard CAN
- Smooth migration at reasonable cost
- Classic CAN and CAN FD LRUs can be mixed under certain conditions
The frame format is different from CAN 2.0. There are two new control bits in the CAN FD frame, the first enabling the new frame format with different data length coding and the second optionally switching to a faster bit rate after the arbitration is decided. New CRC polynomials are introduced to secure the longer CAN FD frames with the same Hamming distance as in the proven CAN protocol. The CAN FD frame format has been defined so that messages in CAN frame format and in CAN FD frame format can coexist within the same network.
BOSCH CAN 2.0
Specification 2.0 remains valid without any modification as an independent, self-contained CAN bus protocol specification. The coexistence is assured by the requirement, that in order to be compatible with this CAN FD specification it is required that a CAN FD implementation be compatible with this CAN FD specification as well as with the BOSCH CAN Specification 2.0.