Xcell Journal: The authoritative journal for programmable ... - Xilinx

In addition to CAN, LIN also complements
Media Oriented Systems Transport
(MOST) for high-speed data rates and
FlexRay for safety-critical applications such
as steer- and brake-by-wire. Figure 1 shows
the relative cost per node and speed of various
automotive networks.
Conceived in 1998, the LIN consortium
comprises car manufacturers Audi,
BMW, DaimlerChrysler, Volvo,
and Volkswagen. LIN is an inexpensive
serial bus used for distributed body control
electronic systems in vehicles. It enables
effective communication for smart sensors
and actuators where the bandwidth and versatility
of CAN is not required. Typical
applications are door control (window lift,
lock, and mirror control), seats, climate regulation,
lighting, and rain sensors. In these
units the cost-sensitive nature of LIN
enables the introduction of mechatronic elements
such as smart sensors, actuators, or
illumination. They can be easily connected
to the car network and become accessible to
all types of diagnostics and services. Outside
the automotive sector, LIN is used for
machine control as a sub-bus for CAN.
A LIN network comprises one master
node and one or more slave nodes. All
nodes include a slave communication task
that is split into 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: the
master sends out a message header that
comprises the synchronization break, synchronization
byte, and message identifier.
Exactly one slave task is activated upon
reception and filtering of the identifier,
which starts the transmission of the message
response. The response comprises two,
four, or 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 destina-
25M
10M
1M
125K
20K
LIN
Time Triggered
Master/Slave
Single Wire, No Crystal
tion. 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.
Flexible LIN Solution
Programmable logic has long been accepted
as an effective way to bring designs to
market quickly and also allow design flexibility
right up to production and beyond.
Historically, this time-to-market advantage
and flexibility had to be balanced with
higher component costs.
But times have changed. PLDs cost
much less and can now be used in highvolume,
cost-sensitive applications such as
mobile phones, PDAs, and automotive infotainment
systems. To enable designs to be
brought to market quickly, some Xilinx
AllianceCORE third-party IP providers
SMARTwireX
Copper Twisted Pair
ByteFlight
FlexRay, TTx
Time Triggered (TDMA)
Fault Tolerant
2 x 2 Wire Optical
CAN-A
Arbitration (CSMA)
Dual Wire
CAN-B
Arbitration
Fault Tol. Dual Wire
Bluetooth
Wireless Bus
1 2 5 10
have developed robust and fully verified IP
cores aimed at FPGA and CPLD architectures.
One example is their LIN core, which
occupies a fraction of a low-cost FPGA (for
example, 13% of a 200,000 system-gate
device), thus leaving space for additional
LIN nodes, CAN nodes, UARTs, soft core
processors, or simply glue logic.
The LIN interface – whether implemented
in programmable logic, ASIC, or
ASSP – is approximately half the cost of a
CAN node.
LIN Bus Benefits
The reliability of LIN is high, but it does
not have to meet the same levels as CAN.
A LIN bus is designed to be a logical
extension to CAN. It is scalable and lowers
the cost of satellite nodes. No crystal
oscillator or resonator is required. It is
easy to implement, has a low reaction
time (100 ms max), and predictable
worst-case timing.
The LIN bus can be implemented using
just a single wire, while CAN needs two
wires. This means that a LIN network can
also be lower in cost through simpler connectors
and wiring – thus also reducing the
Winter 2004 Xcell Journal 93
J1850
D2B, MOST
Token Ring
Optical Bus
Figure 1 – Relative cost per node of automotive networks
Programmable logic has long been accepted as an effective way to bring
designs to market quickly and also allow design flexibility...