#lin stack

The LIN Bus protocol has built in master/slave architecture. It is a polled bus with one or more slave devices and a single master device. A master task and a slave task are both present on the master device. Each slave device only has one slave task. The master task in the master device controls all communication over the LIN bus.

The LIN Bus Frame Format

The frame, which is divided into a header and a response, is the basic unit of transfer on the LIN bus. The master node always sends the header, which contains three separate fields: the break, synchronization (sync), and identifier (ID). A slave task transmits the response, which includes a data payload and a checksum and can remain on either the master or slave node.

[Image source: Engineer Ambitiously]

A message comprises the following fields:

1.       Synchronization Break

2.       Synchronization Byte

3.       Byte Identifier

4.       Data Bytes

5.       Checksum Byte

The LIN Bus Protocol Frame types

Unconditional Frame: These frames always carry signals and have IDs ranging from 0 to 59 (0x00 to 0x3b)

Event-driven frame: The goal is to improve the responsiveness of the LIN cluster without allocating too much bus capacity to polling numerous slave nodes with infrequent events. The conveyed unconditional frame's initial data byte must be equivalent to a protected identification provided to an event-triggered frame.

Sporadic Frame: The master transmits this frame when needed, preventing a collision. A sporadic frame's header must be transmitted in its corresponding frame slot only when the master task is aware that a signal conveyed in the frame has been modified. The answer to the header must always be sent by the publisher of the sporadic frame.

The diagnostic Frame: These always include eight data bytes and always convey diagnostic or configuration data. The identification is either 60 (0x3C), which is known as the master request frame, or 61 (0x3D), which is known as the slave response frame.

User Specified or User Defined Frame: These frames can contain any type of data. Their identification number is 62 (0x3E). The header of a frame slot is always transmitted when a particular frame slot under a frame is being extracted.