CiA® 601 series: CAN FD guidelines and recommendations

This series of guidelines and recommendations fills the gap between the ISO standard for CAN FD and the system design. Part 1 provides specifications and guidelines on the physical layer interface design for automotive electronic control units and non-automotive devices supporting the CAN FD data link layer as defined in ISO 11898-1 and the CAN high-speed physical layer as defined in the harmonized ISO 11898-2 standard, which includes the specification of high-speed transceivers with low-power mode (formerly known as ISO 11898-5) and/or with selective wake-up functionality (formerly known as ISO 11898-6).

Sampling of a recessive bit at the transmitting node with and without transmitter delay compensation (TDC)

Part 1 is published as a Draft Standard (DS). It specifies the Tx delay symmetry and the Rx delay symmetry requirements as well as the recessive bit-time at the receiving node's RxD pin for different bit-rates (1 Mbit/s, 2 Mbit/s, and 5 Mbit/s). Rules of thumb for how to calculate the transmitter delay with and without galvanic isolation are also included. Part 1 will be updated depending on the experiences coming from prototype developments of OEMs and CAN FD plugfest organized by CiA.

Part 2 describes the specified interface between the protocol controller implementing the CAN FD data link layer protocol and the host controller including necessary configuration registers. It specifies the finite state automaton of the CAN controller, which describes its behavior. The properties, type and configuration of the receive message buffers and of the transmit message buffers as well as the acceptance filtering are also specified. Additionally, the interrupt source registers are described. The configuration range for the timing parameters in the bit-timing registers in the arbitration phase respectively in the data phase and the configuration range of the SSP (secondary sample point) position are also recommended. Such a harmonized interface reduces the effort for adapting the low-level driver software to different implementations. Part 2 is published as a Draft Standard Proposal (DSP).

Part 3 provides rules and background information about the setting of bit-times in CAN FD networks. This document is published as a DSP, and will be reviewed after about one year. In the review process made experiences are considered. The CiA 601-3 comes with a spreadsheet to support the network designer to check, whether your selected bit-rates are possible. CAN FD frames are transmitted with two bit-rates. The rules for the arbitration bit-rate are the same as for Classical CAN. In the data phase additional rules have to be considered for a robust communication, e.g. the phase margin for received and transmitted frames. The released document contains all the necessary formulas to calculate the limits. In addition, it proposes, how to measure them. This document recommends also some optimization hints for the phase margin. It includes recommendations for the topology, and the node design.

Part 4 is published as a DSP and specifies a ringing suppression circuitry (RSC) for CAN FD networks. It is intended for single-star or multiple-stars topologies and hybrid topologies. The RSC can be implemented in the CAN transceiver, or connected to the CAN transceiver as an external circuitry. A new version of the CiA 601-4 is under review, which specifies the signal improvement behavior. It is planned to release it within 2018.

Non-members can purchase the CiA 601-1, CiA 601-2, CiA 601-3, and CiA 601-4 documents. Please send an email to secretary(at)can-cia.org.