An Efficient Fixed-Length Encoding Scheme for CAN

Because of the bit stuffing mechanism CAN relies on, the actual duration of frame transmissions over the bus depends on the specific value carried in the data field of the frames. This causes jitters on reception times, which may worsen timing accuracy. Sometimes, this behavior cannot be accepted and a number of approaches have been conceived to overcome this problem. In this paper, a software-based technique is described that consists of encoding the payload of the frame before its transmission by using a suitable 8B9B scheme. Such an approach ensures that no stuff bit has then to be added in h/w by the CAN controller. In this way, jitters are either prevented or, at least, reduced noticeably. The proposed algorithm is very simple and can be implemented, easily and efficiently, on low-cost embedded architectures too.