An Automotive Specification of a Time Triggered CAN Implementation: Doubling CAN's Usable Data Throughput

The Controller Area Network (CAN) has seen enormous success in automotive body and powertrain control systems, and in industrial automation systems using higher layer protocols such as DeviceNet and CANopen. Now, the CAN standard ISO11898 are being extended to Time Triggered CAN (TTCAN) to address the safety critical needs of first generation drive-by-wire systems. However, their successful development depends upon the availability of silicon and software support, and appropriate development & analysis tools. This paper outlines the current status of TTCAN technology and describes the implementation of Level 1 TTCAN on the Atmel 89c51cc01/cc02/cc03/cc04 microcontrollers. The descriptions contained show how to implement for different bus speeds, along with suggestion for a user to tailor the drivers for their own application. Level 2 TTCAN is also described for comparison purposes.

Whilst the TTCAN implementation described in this paper is limited to the maximum CAN bit rate of 1Mbit/s, TTCAN can be used to effectively double the bandwidth of a CAN system to the region of 60 to 70% bus loading at 500 Kbit/s and 1Mbit/s. This is approximately twice that of traditional automotive CAN systems. For example, a typical automotive power train control system based on CAN typically runs at maximum of about 35% loading at 500 KBaud to avoid data bus latencies.