Datasheet

BRK_count
SDEL
BAUD_count
SYNCH BREAK
SYNCH FIELD
10 Tbit
ID FIELD
10 Tbit
START BIT
STOP BIT
0
1
01
01
01
1 2 3 4
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28.3.1.5.2 Header Reception and Adaptive Baud Rate
A slave node baud rate can optionally be adjusted to the detected bit rate as an option to the LIN module.
The adaptive baud rate option is enabled by setting the ADAPT bit. During header reception, a slave
measures the baud rate during detection of the synch field. If ADAPT bit is set, then the measured baud
rate is compared to the slave node’s programmed baud rate and adjusted to the LIN bus baud rate if
necessary.
The LIN synchronizer determines two measurements: BRK_count and BAUD_count (Figure 28-17). These
values are always calculated during the Header reception for synch field validation (Figure 28-18).
Figure 28-17. Measurements for Synchronization
By measuring the values BRK_count and BAUD_count, a valid synch break sequence can be detected as
described in Figure 28-18. The four numbered events in Figure 28-17 signal the start/stop of the
synchronizer counter. The synchronizer counter uses VCLK as the time base.
The synchronizer counter is used to measure the synch break relative to the detecting node T
bit
. For a
slave node receiving the synch break, a threshold of 11 T
bit
is used as required by the LIN protocol. For
detection of the dominant data stream of the synch break, the synchronizer counter is started on a falling
edge and stopped on a rising edge of the LINRX. On detection of the synch break delimiter, the
synchronizer counter value is saved and then reset.
On detection of five consecutive falling edges, the BAUD_count is measured. Bit timing calculation and
consistency to required accuracy is implemented following the recommendations of LIN revision 2.0. A
slave node can calculate a single T
bit
time by division of BAUD_count by 8. In addition, for consistency
between the detected edges the following is evaluated:
BAUD_count + BAUD_count » 2 + BAUD_count » 3 ≤ BRK_count
The BAUD_count value is shifted 3 times to the right and rounded using the first insignificant bit to obtain
a T
bit
unit. If the ADAPT bit is set, then the detected baud rate is compared to the programmed baud rate.
During the header reception processing as illustrated in Figure 28-18, if the measured BRK_count value is
less than 11 T
bit
, the synch break is not valid according to the protocol for a fixed rate. If the ADAPT bit is
set, then the MBRS is used for measuring BRK_count and BAUD_count values and automatically adjusts
to any allowed LIN bus rate (refer to LIN Specification Package 2.0).
NOTE: In adaptive mode the MBRS divider should be set to allow a maximum baud rate that is not
more than 10% above the expected operating baud rate in the LIN network. Otherwise, a
0x00 data byte could mistakenly be detected as a synch break.
The break-threshold relative to the slave node is 11 T
bit
. The break is 13 T
bit
as specified in
LIN version 1.3.
1370
Serial Communication Interface (SCI)/Local Interconnect Network (LIN) SPNU562–May 2014
Module
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