Improving information throughput and transmission predictability in Controller Area Networks

The Controller Area Network (CAN) protocol was originally developed for distributed automotive applications in the 1980s, and has previously proved to be extremely popular for the implementation of low-cost distributed systems. Whilst CAN has many features that make it suitable for such applications, it also has a number of well-discussed drawbacks; data transmission is limited to a fixed 8-byte payload at 1 Mbps, and the hardware bit-stuffing mechanism and automatic retransmission scheme can act to severely decrease the predictability of a CAN network. This paper will describe a modified CAN-like protocol controller that can be implemented on a programmable-logic device such as an FPGA. The modified protocol controller can help to ameliorate one of the drawbacks of CAN, whilst operating as closely as is possible to the original protocol specification. Specifically, this paper will discuss an implementation of a simple extension to the original protocol that allows for larger payloads, coupled with modifications to the bit-stuffing mechanism to increase predictability. The effectiveness of this modified CAN controller is illustrated in a series of experiments employing a novel test facility. The paper also discusses the potential drawbacks of the new controller, and is then concluded by suggesting possible areas of further research.