Courtesy: ISO 17987 road vehicles local interconnect network (LIN)
BREAK: The BREAK field is used to activate all attached LIN slaves to listen to the following parts of the header. It consists of one start bit and several dominant bits. The length is at least 11-bit times; standard use as of today are 13-bit times, and therefore differs from the basic data format. This is used to ensure that listening LIN nodes with a main-clock differing from the set bus baud rate in specified ranges will detect the BREAK as the frame starting the communication and not as a standard data byte with all values zero (hexadecimal 0x00).
SYNC: The SYNC is a standard data format byte with a value of hexadecimal 0x55. LIN slaves running on RC oscillator will use the distance between a fixed amount of rising and falling edges to measure the current bit time on the bus (the master’s time normal) and to recalculate the internal baud rate.
INTER BYTE SPACE: Inter Byte Space is used to adjust for bus jitter. It is an optional component within the LIN specification. If enabled, then all LIN nodes must be prepared to deal with it.
There is an Inter Byte Space between the BREAK and SYNC field, one between the SYNC and IDENTIFIER, one between the payload and Checksum and one between every Data byte in the payload.
IDENTIFIER: The IDENTIFIER defines one action to be fulfilled by one or several of the attached LIN slave nodes. The network designer has to ensure the fault-free functionality in the design phase (one slave is allowed to send data to the bus in one frame time).
If the identifier causes one physical LIN slave to send the response, the identifier may be called a Rx-identifier. If the master’s slave task sends data to the bus, it may be called Tx-identifier.
RESPONSE SPACE: Response Space is the time between the IDENTIFIER field and the first Data byte which starts the LIN RESPONSE part of the LIN frame. When a particular LIN frame is transmitted completely, Header + Response, by the LIN MASTER, the LIN MASTER will use the full RESPONSE SPACE TIME to calculate when to send the response after sending the header. If the response part of the LIN frame is coming from a physically different SLAVE NODE, then each node (master & slave) will utilize 50% of the Response Space time in their timeout calculations.
ISO 17987-2:2016 specifies a transport protocol and network layer services tailored to meet the requirements of LIN‑based vehicle network systems on local interconnect networks. The protocol specifies an unconfirmed communication.
The LIN protocol supports the standardized service primitive interface as specified in ISO 14229‑2.
ISO 17987-2:2016 provides the transport protocol and network layer services to support different application layer implementations like
– normal communication messages, and
– diagnostic communication messages.
The transport layer defines transportation of data that is contained in one or more frames. The transport layer messages are transported by diagnostic frames. A standardized API is specified for the transport layer.
Use of the transport layer is targeting systems where diagnostics are performed on the backbone bus (e.g. CAN) and where the system builder wants to use the same diagnostic capabilities on the LIN sub-bus clusters. The messages are in fact identical to the ISO 15765‑2 and the PDUs carrying the messages are very similar.
The goals of the transport layer are
– low load on LIN master node,
– to provide full (or a subset thereof) diagnostics directly on the LIN slave nodes, and
– targeting clusters built with powerful LIN nodes (not the mainstream low cost).