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.

CiA 601-1 (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. This standard includes the specification of CAN 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). 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.

CiA 601-2 (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 DS.

CiA 601-3 (part 3) provides rules and background information about the setting of bit times in CAN FD networks. This document is published as a DS. 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 also recommends some optimization hints for the phase margin. It includes recommendations for the topology, and the node design.

In order to enable the use of not ideal topologies, the data phase bit rate needs to be lowered. Another option is to use so-called SIC (signal improvement capability) transceivers, which suppress the ringing caused by the not optimized network topology. These SIC transceivers are specified in CiA 601-4 (part 4). There are two implementations available: one suppresses the ringing when transmitting; the other filters the ringing when receiving. Part 4 is published as a DS and specifies additional requirements for HS-PMA implementations compliant with ISO 11898-1:2015 and ISO 11898-2:2016 for the purpose of reducing differential and common-mode ringing on the CAN_H and CAN_L wires, especially for the transition from dominant to recessive state. The intent of this specification is to enable larger topology flexibility and higher bit rates for CAN networks. The HS-PMA implementations with additional signal improvement functionalities support communication in the presence of defined unterminated wire stubs without requiring configuration, for example bit rate settings. Furthermore, this document specifies EMC (electromagnetic compatibility) tests for HS-PMA implementations with additional signal improvement functionalities.

CiA 601-6 (part 6) CAN FD cable is published as a DS and specifies requirements and test methods of mechanical and electrical parameters for cables to be used in CAN FD networks. In general, the specification refers to the ISO 6722 series standardizing single-core cables for 60-V to 600-V in road vehicles. In this CiA document, bending radius and twist-rate are specified, for example. Additionally, impedance tolerance, specific cable delay, insertion loss, and ohmic DC-resistance per length are given. The symmetry of cable by means of transverse conversion loss is specified for different frequencies.

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