LIN (Local Interconnect Network)
1.0 What is LIN?
LIN is a serial communication protocol, which is more cost- sensitive used in
automotive applications.
2.0 LIN basic Layout:
LIN cluster
A LIN Cluster consists of a number of nodes that are interconnected via a physical transmission
medium (see figure: Network). A general distinction is made between two types of nodes. There is
always a master that controls bus access, and there are multiple slaves that can send and receive
information.
LIN communication controller:
In LIN no dedicated communication controller was implemented. Instead, the protocol must be
integrated as a software component in the microcontroller. It should be clearly noted whether a node
is to be implemented as the master or a slave. The microcontroller is connected to the transceiver via
the serial interface.
LIN Transceiver:
The transceiver serves to physically connect the bus to the network. This chip converts the logical bit
sequence into transmittable bus levels and in the reverse direction. While the TX section is used to
generate the voltages on the bus, the Rx section enables evaluation of the received levels.
Physical Layer:
In LIN, physical signal transmission only requires one conductor (single wire). To maintain
radiated electrical emissions within limits, the transmission rate is limited to 20 kBit/s for
LIN.
Another restriction is the maximum recommended number of 16 nodes.
Serial Interface
Controller Interface
The transceiver is connected via the microcontroller’s integrated serial interface. This is
known as the SCI.
Data Transmission
Serial data transmission in a cluster is byte-oriented. The SCI transmits the least significant
bit (lsb) of each byte first, which is framed by a start bit and a stop bit. This combination of
ten bits is referred to as an SCI frame. A message is composed of multiple SCI frames (see
figure: Frame)
SCI Frame
Each SCI Frame begins with a dominant Start bit, which causes a falling edge that is used by
all receivers for resynchronization.
Signal transmission in LIN:
Single Wire
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No differential voltage signals can be used for physical signal transmission.
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Instead, a conventional single-wire line (single wire) is used with defined voltage
levels for logic one and logic zero.
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The typical topology is a line bus.
Voltage and Logical Levels
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A level of less than 40% of the supply voltage is interpreted as a logic zero by the
receiver.
The receiver interprets as logic one all levels that lie above 60% of the supply voltage.
Senders transmit a voltage level below 20% for logic zero.
A voltage level above 80% for logic one.
Sender:
Communication principle in LIN:
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Communication in a LIN cluster is based on a master-slave architecture.
There is always one node which, as master, controls all communication between the various
slaves.
Message Types:
There are a total of four message types, which are known as the
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Unconditional Frame
Sporadic Frame
Event Triggered Frame
Diagnostic Frame.
Unconditional Frame:
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The unconditional frame is typically used to transmit useful data.
This message type corresponds to the standard frame.
The unconditional frame consists of a header and a response.
The master transmits the header onto the bus as a request. Then a defined slave answers with
the response.
A Slave Task recognizes, based on the identifier (ID), whether it needs to send a response.
ID value between 0 to 59.