MODULE - 10
Communication Interfaces Continued:
LIN (Local Interconnect
LIN (Local Interconnect Network) was developed as cost-effective
alternate to CAN protocol. In 1998 a group of companies
including Volvo, Motorola, Audi, BMW, Daimler Chrysler,
and Volkswagen formed a consortium to develop LIN.
The latest version of LIN is LIN 2.0 and was released in
2003. LIN 2.0 provides interesting features such as diagnostics.
The LIN is a SCI/UART-based serial, byte-oriented, time
triggered communication protocol designed to support automotive
networks in conjunction with Controller Area Network (CAN),
which enables cost-effective communication with sensors
and actuators when all the features of CAN are not required.
The main features of this protocol (compared to CAN) are
low cost and low speed and used for short distance networks.
Usually in automotive application, the LIN bus is connected
between smart sensor or actuators and an Electronic Control
Unit (ECU) which is often a gateway with CAN bus. Like CAN,
LIN is also a broadcast type serial network, but with single
master and multiple (up to 16) slaves. No collision detection
exists in LIN, therefore all messages are initiated by the
master with at most one slave replying for a given message
identifier. The master is typically a moderately powerful
microcontroller, whereas the slaves can be less powerful,
cheaper micro-controllers or dedicated ASICs.
Moreover the LIN is a single wire 12V bus connection, in
which the communication protocol is based upon ISO 9141
NRZ-standard. An important feature of LIN is the synchronization
mechanism that allows the clock recovery by slave nodes
without quartz or ceramics resonator. Only the master node
will be using the oscillating device. Nodes can be added
to the LIN network without requiring hardware or software
changes in other slave nodes. And the maximum transmission
speed will be 20kbit/s.
How do they transmit & receive data?
As we have already seen, the LIN network comprises of one
master node and one or more slave nodes. Only the master
node initiates the communication in a LIN network. The master
node defines the transmission speed, sends synchronization
pulses, and does data monitoring and switching slave nodes
to sleep/wake up mode. It also receives Wakeup Break from
slave nodes when the bus is inactive and they request some
A slave node waits for the synchronization pulse, and then
does synchronization using synchronization pulse and process
the message identifier. Then according to the ID, the slave
decides what to do, either to receive data or to transmit
or to do nothing. While transmitting it sends 2, 4 or 8
data bytes depending on the ID received, plus a checksum
byte. The two types of data messages in the LIN network
are the signal message (data which are sent in the data
frame) and the diagnostic message.
The network consists of one master task and several slave
tasks. In the master node the both tasks- master & slave
can be found, but in a slave node the slave task only.
The communication can take place 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.
The communication is also possible directly from slave to
slave without routing through the master node.
The LIN uses frames for data communication. A frame consists
of a header, a response and some response space so the slave
will have time to answer. The master sends out a message
header, or in other words the headers are situated in a
master task, contains synchronization breaks, synchronization
byte and the message identifier, each part begins with a
start bit and ends with a stop bit. The response contains
one to eight data bytes and one checksum byte. The slave
task is connected to the identifier and receives the response,
verifies the checksum and uses the data transport. Messages
are created when the master node sends a frame containing
a header. The slave node(s) then fills the frame with data
depending on the header sent from the master.
This system of communication using headers and responses
has a lot of advantages. Some of them are
1. The nodes can be added to the network without requiring
hardware or software changes in other slave nodes.
2. The identifier defines the content of a message and
3. Any number of nodes can simultaneously receive and act
upon a single frame.
The LIN protocol is byte oriented, which means that data
is sent one byte at a time. One byte field contains a start
bit (dominant), 8 data bits and a stop bit (recessive).
The data bits are sent LSB first.
The synch break is the beginning of a Message Frame. It
contains at least 13 bits of dominant value including the
start bit followed by at least 1 bit long recessive break
delimiter. The synch byte or the synch field is used to
determine the time between two rising edges to determine
the transmission rate which the master node uses.
The identifier of a message, which is 6-bits long identifier
plus 2 parity bits, denotes the content of a message but
not the destination. It incorporates information about the
sender, the receivers, the purpose, and the data field length
of the response (The three classes of 2/4/8 data bytes).
The length coding is done in the 2 MSB of the ID-Field.
A total of 64 message Identifiers is possible here. The
two linked parity bits are used to protect this ID-field.
The parity bits can be calculated as explained below:
P0 = XOR of bits ID0, ID1, ID2 and ID4.
P1 = NOT of XOR of bits ID1, ID3, ID4 and ID5.
The length of the response data field from the slave can
be 2, 4 or 8 bytes, depending on the two MSB of the ID field
send by the master node (LIN 1.3 have length of 8-bytes
There are two types of checksum used in LIN. The first
one used in LIN 1.3 consists of the inverted eight-bit sum
of all 8 data bytes in a message. The new checksum used
in LIN 2.0 also incorporates the protected identifier in
the checksum calculation.
The power management in LIN network:
The network management in a LIN cluster contains "wake
up" and "go-to sleep".
All the slave nodes in an active LIN cluster can be changed
into sleep mode by sending a diagnostic master request frame
with the first data byte equal to zero. This special use
of a diagnostic frame is called a go-to-sleep-command. Slave
nodes can automatically enter a sleep mode if the LIN bus
is inactive for more than 4 seconds.
Any node in a sleeping LIN cluster can send a request for
wake up cluster. The wake-up request can change the bus
to the dominant state for 250 ms to 5 ms.
Every slave node can detect the wake-up request (a dominant
pulse longer than 150 ms) and be ready to listen to bus
commands within 100 ms, measured from the ending edge of
the dominant pulse.
The master node can also wake up and, when the slave nodes
are ready, start sending frame headers to find out the cause
of the wake up. If the master does not gain frame headers
within 150 ms from the wake up request, the node sending
the request can try to send a new wake up request. After
three failing requests the node shall wait minimum 1.5 seconds
before sending a fourth wake up request.
LIN Versus CAN:
There is no meaning of comparing CAN and LIN since they
do not address the same issues. However it can give you
a general view of LIN in the big picture.
As we already saw, the LIN targets low-end applications
where the communication cost per node must be two to three
times lower compared to CAN but where the performance, robustness
and versatility of CAN are not required. The main economical
factor in favor of LIN is the avoidance of high cost quartz
or ceramic resonators in slave nodes, as they can perform
self-synchronization. A small comparative study gives the
|Media access control
| Bus Speed
||2.4, 9.6 and 19.2 Kbps
||62.5Kbps to 1Mbps
||6 bit identifier
||11/29 bit identifier
|Size of network
||2 to 16 nodes
||4 to 20 nodes
|Data Byte per Frame
||0 to 8
||2 to 8
|Transmission time for 4 data bytes
||6 ms at 19.2Kbps
||0.8 ms at 125Kbps
|Error detection(Data field)
||15 bit CRC
||Single wire, 40V
||Shielded,Twisted pair, 5V
||For master only
||For All nodes
Some of the main drawbacks of LIN are lower bandwidth and
less effective bus access scheme with the master- slave
To learn more about LIN click below urls:
a LIN Master Node Driver on a PIC18 Microcontroller with
to LIN (Local Interconnect Network) Stéphane REY
Module - 11(I2C)
Module - 9(CAN)
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