THE LIN CONCEPT
FEATURES
LIN is a single-wire serial communications protocol based on the common SCI (UART) byte-word interface. UART interfaces are available as low cost silicon module on almost all micro-controller and can also be implemented as equivalent in software or pure state machine for ASICs. The medium access in a LIN network is controlled by a master node so that no arbitration or collision management in the slave nodes is required, thus giving a guarantee of the worst-case latency times for signal transmission.
A particular feature of LIN is the synchronization mechanism that allows the clock recovery by slave nodes without quartz or ceramics resonator. The specification of the line driver and receiver is following the ISO 9141 single-wire standard with some enhancements. The maximum transmission speed is 20 kbit/s, resulting from the requirements by electromagnetic compatibility (EMC) and clock synchronization.
A node in LIN networks does not make use of any information about the system configuration, except for the denomination of the master node. Nodes can be added to the LIN network without requiring hardware or software changes in other slave nodes. The size of a LIN network is typically under 12 nodes (though not restricted to this), resulting from the small number of 64 identifiers and the relatively low transmission speed. The clock synchronization, the simplicity of UART communication, and the single-wire medium are the major factors for the cost efficiency of LIN.
A particular feature of LIN is the synchronization mechanism that allows the clock recovery by slave nodes without quartz or ceramics resonator. The specification of the line driver and receiver is following the ISO 9141 single-wire standard with some enhancements. The maximum transmission speed is 20 kbit/s, resulting from the requirements by electromagnetic compatibility (EMC) and clock synchronization.
A node in LIN networks does not make use of any information about the system configuration, except for the denomination of the master node. Nodes can be added to the LIN network without requiring hardware or software changes in other slave nodes. The size of a LIN network is typically under 12 nodes (though not restricted to this), resulting from the small number of 64 identifiers and the relatively low transmission speed. The clock synchronization, the simplicity of UART communication, and the single-wire medium are the major factors for the cost efficiency of LIN.
COMMUNICATION CONCEPT
A LIN network comprises one master node and one or more slave nodes. All nodes include a slave communication task that is split in a transmit and a receive task, while the master node includes an additional master transmit task. The communication in an active LIN network is always initiated by the master task as illustrated in the figure below: the master sends out a message header which comprises the synchronization break, the synchronization byte, and the message identifier.
Exactly one slave task is activated upon reception and filtering of the identifier and starts the transmission of the message response. The response comprises one to eight data bytes and one checksum byte. The header and the response part form one message frame.
Exactly one slave task is activated upon reception and filtering of the identifier and starts the transmission of the message response. The response comprises one to eight data bytes and one checksum byte. The header and the response part form one message frame.
The identifier of a message denotes the content of a message but not the destination. This communication concept enables the exchange of data in various ways: from the master node (using its slave task) to one or more slave nodes, and from one slave node to the master node and/or other slave nodes. It is possible to communicate signals directly from slave to slave without the need for routing through the master node, or broadcasting messages from the master to all nodes in a network. The sequence of message frames is controlled by the master and may form cycles including branches.
