Generic bit-timing settings for CAN FD

There are two bit-timing settings required in CAN FD networks for the nominal and the data bit-time.

The bit-timing settings in “open” CAN FD networks are more tricky. Not just two bit-times need to be configured, it is also the combination of both, which is to be selected. There are several design rules and recommendation to be considered. CiA members discuss, how a generic bit-timing setting should look like. It is intended to limit the freedom, the flexibility, in order to make it as simple as possible.

The bit-timing in the arbitration phase and in the data phase shall use the very same time quanta, the same oscillator frequency, the very same sample-points. It is also required to enable the Transceiver Loop-delay Compensation (TDC).

CiA had already distributed a CAN FD physical layer requirements questionnaire, but the responses were just a few. The intended generic bit-timing settings should be independent of the higher-layer protocol (e.g. CANopen FD or J1939 on CAN FD as specified in CiA 602-2).

CiA also discusses the need of a CAN FD cable specification for dedicated applications (e.g. automotive and industrial). This is a complicated topic. Nevertheless, parameter definitions and parameter testing could be specified, in order to make datasheets comparable.

Volunteers, proposals, and desires are welcome. Address them please to Holger Zeltwanger (secretary(at)