SLLA521B January 2022 – June 2022 TCAN1145-Q1 , TCAN1146-Q1
This application note discusses selective wake-up as per ISO 11898-2:2016 and how it enables partial networking (PN). The application note includes how PN is used, how to configure TI devices, and two set-up examples.
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Controller Area Network (CAN) is a communication architecture used for reliable communication in environments that are considered to be noisy, one example being automobiles. Over time, CAN has evolved to include classic high-speed CAN as well as CAN flexible data rate (CAN FD). Classic high-speed CAN supports data rates up to 1 Mbps and although CAN FD is backwards compatible with classic high-speed CAN, it also supports data rates up to 5 Mbps and higher. CAN FD supports up to 64 bytes and a bit rate switching mode, which allows faster than 1 Mbps data transmission.
In an automotive CAN network, power is always a concern for situations when the vehicle is off or when only a few electrical control units (ECUs) need to be on during normal operation. The development of PN addresses this concern. PN is a method used to save power when both homogeneous (all ECUs capable of PN) or mixed (not all ECUs capable of PN) CAN and CAN FD networks are used. This process is accomplished by allowing bus communication, but sleeping nodes only wake on a specific CAN message or frame. PN was developed by the International Standard Organization (ISO) and is based upon the latest version of the ISO 11898-2:2016 standard.
This application note provides information using an example application. The application note focuses on what selective wake, also known as partial networking (PN), is and how it is used in an application. The register set from the TCAN1145-Q1 and TCAN1146-Q1 is provided for ease of understanding and finishes with two examples on how to program a device for PN.
Figure 2-1 represents a simplified mixed CAN FD network. ECU3 and ECU6 are partial networking capable ECUs. The rest of the ECUs are not PN capable. ECU1 and ECU8 represent the termination locations. CAN bus represents the CANH and CANL signals. PN enabled ECUs described in the following sections relate to ECU3 and ECU6 in this figure.
To understand partial networking in an application the PN capable CAN transceiver needs to be understood. Modes of operation and the impact of partial networking will be presented, followed by a deeper investigation of sleep mode and how utilizing PN creates two different levels of sleep. To understand how PN works, a brief explanation on a CAN frame is provided which will be followed up with a more detailed explanation. Lastly, information will be provided on how a mixed network similar to the simplified one provided will behave.