AN2103 Freescale Semiconductor / Motorola, AN2103 Datasheet - Page 3

• Manufacturer Part Number: AN2103
• Description: Local Interconnect Network (LIN) Demonstration
• Manufacturer: Freescale Semiconductor / Motorola

AN2103
MOTOROLA
2.1 Header
Frame
The master controls all bus traffic on the network. The master initiates
communication by transmitting a header frame with synchronization and
identifier information. Any slave, including the slave task in the master
control unit, can respond with a data frame. Only one slave can respond
to each identifier. However, any number of slaves can be configured to
recognize a particular identifier driven on the bus. The master control
unit can transfer data to any number of slaves through its slave task. i.e.
the master’s slave task responds to a header (sent by the master) and
transmits data on to the bus. All other slaves can simultaneously receive
the data frame.
The header frame consists of 3 main parts: a SYNCH BREAK signal, a
SYNCH FIELD and an IDENTIFIER. The SYNCH BREAK is used to
identify the beginning of a message frame and allow the slaves to
synchronise to the master’s bus clock. It is a unique signal that has 2
parts: a Dominant SYNCH BREAK that is longer than any regular
dominant bit stream, and a synchronisation delimiter that is required to
enable the detection of the start bit of the following SYNCH FIELD.
Figure 2
The timing specification for the SYNCH_BREAK field is dependent on
the tolerance of the slave node’s clock source. The master is always
required to transmit a dominant T
measured in the master’s time base. The slave detects a break signal if
it is dominant for longer than any regular bit stream. If the slave’s clock
source has a tolerance lower than +- 15% (F
BREAK THRESHOLD is 11 bit times (number of dominant bits required
to be recognised as a SYNCH BREAK FIELD) measured in the slave’s
time base. If the clock source’s tolerance is less than +- 2% (F
) the threshold is reduced to 9 dominant bits.
The second part of the header is the SYNCH FIELD that contains the
pattern 0x55 to allow the slave to synchronize with the master. This
Freescale Semiconductor, Inc.
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Figure 2 SYNCH BREAK field
shows the SYNCH BREAK field.
TSYNBRK
SYNCH BREAK
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FIELD
SYNBRK
TSYNDEL
signal, that is a minimum 13 bits,
Local Interconnect Network Bus (LIN)
TOL_UNSYNCH
SYNCH
FIELD
) the SYNCH
Header Frame
TOL_SYNCH
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