Introduction to LIN

Data transmission of user data in a LIN cluster generally involves use of the so-called unconditional frame. The unconditional frame is composed of a frame header together with a frame response. The LIN master is responsible for transmitting the frame header. The frame response is transmitted by a slave task defined in the LDF.

As can be seen in the figure “LIN Frame”, a frame header begins with transmission of a synchronization symbol (Sync Break Field) and should make all LIN slaves in the LIN cluster aware of the beginning of transmission of a LIN frame. Following the sync break field there is the sync field for establishing a common clock between the LIN slaves.

Once communication has been initiated and the LIN slaves have synchronized, the LIN master transmits an identifier (ID) to delegate the communication. Two parity bits protect the ID. The parity bits together with the ID form the protected identifier (PID).

Immediately after the frame header, the LIN slave addressed by the identifier transmits the associated frame response (in some cases the frame response may also be sent by the LIN master's slave task). A maximum payload of eight bytes can be transmitted with a frame response. Transmission of the frame response ends with transmission of a checksum, which protects the user data (see figure “LIN Frame”).

LIN communication technology was developed to save on costs. To enable the use of low-cost and therefore less powerful microcontrollers, the LIN protocol specifies a time reserve of up to 40% for transmission of LIN frames, which must absolutely be considered in the system design.

If necessary, each LIN node can delay the transmission of SCI frames, which leads to transmission pauses between SCI frames. These are called the interbyte space. If transmission of the frame response is delayed, one speaks of a response space. The animation “LIN Frame Transfer” explains this subject matter.

You can take advantage of the animation “Unconditional Frame” to practice the use of unconditional frames. Read the instructions so that you can utilize the full functionality of the animation.

To reinforce and deepen your knowledge of the unconditional frame, an exercise is provided for you as well. It asks you to calculate the parameters that define an unconditional frame, based on randomly generated exercise values. Please read the instructions so that you can fully utilize the entire functionality of the exercise.