CAN with Flexible Data-Rate

Abstract

Ever increasing bandwidth requirements in automotive networks impede the applicability of CAN due to its bit rate limitation to 1 MBit/s. To close the gap between CAN and other protocols, we improve CAN in two ways: (i) support of bit rates > 1 MBit/s and (ii) support of payloads > 8 byte per frame. We achieve this with a new frame format where we can switch inside the frame to a faster bit rate for (i) and use a different data length coding for (ii). This new protocol is called “CAN with Flexible Data-Rate” or CAN FD. CAN FD protocol controllers are also able to perform standard CAN communication. This allows to use CAN FD in specific operation modes, e.g. softwaredownload at end-of-line programming, while other controllers that do not support CAN FD are kept in standby. This paper presents the CAN FD frame format with additional bits in the control field to enable the new options and the new CRC sequence to secure longer frames with the same Hamming distance as in the existing CAN protocol. The configuration options for the two bit rates are explained in detail. We provide measurements of the upper limits for the bit rate, using the first hardware implementation of a CAN FD protocol controller and standard CAN transceivers.