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minimum pulse width required. In this case the first bit is accepted as a '0', the second bit
is a '1', and the third bit is also a '1'. A low pulse is rejected since it does not meet the
minimum requirement of 2/16 baud clock.
Figure 34-11. IrDA Receive Decoding
IrDA encoded RXD
RXD
Baud clock
20 SE clock cycles
0 0.5
1
1.5
2 2.5
34.6.3.4 Break Character Detection and Auto-Baud/LIN Slave
Break character detection and auto-baud are available in this configuration:
• Auto-baud frame format (CTRLA.FORM = 0x04 or 0x05),
• Asynchronous mode (CTRLA.CMODE = 0),
• and 16x sample rate using fractional baud rate generation (CTRLA.SAMPR = 1).
The USART uses a break detection threshold of greater than 11 nominal bit times at the configured baud
rate. At any time, if more than 11 consecutive dominant bits are detected on the bus, the USART detects
a Break Field. When a break field has been detected, the Receive Break Interrupt Flag
(INTFLAG.RXBRK) is set and the USART expects the sync field character to be 0x55. This field is used
to update the actual baud rate in order to stay synchronized. If the received sync character is not 0x55,
then the Inconsistent Sync Field error flag (STATUS.ISF) is set along with the Error Interrupt Flag
(INTFLAG.ERROR), and the baud rate is unchanged.
The auto-baud follows the LIN format. All LIN Frames start with a Break Field followed by a Sync Field.
Figure 34-12. LIN Break and Sync Fields
Break Field
Sync Field
8 bit times
After a break field is detected and the Start bit of the sync field is detected, a counter is started. The
counter is then incremented for the next 8 bit times of the sync field. At the end of these 8 bit times, the
counter is stopped. At this moment, the 13 Most Significant bits of the counter (value divided by 8) give
the new clock divider (BAUD.BAUD), and the 3 Least Significant bits of this value (the remainder) give
the new Fractional Part (BAUD.FP).
When the sync field has been received, the clock divider (BAUD.BAUD) and the Fractional Part
(BAUD.FP) are updated after a synchronization delay. After the break and sync fields are received,
multiple characters of data can be received.
34.6.3.5 LIN Master
LIN master is available with the following configuration:
• LIN master format (CTRLA.FORM = 0x02)
• Asynchronous mode (CTRLA.CMODE = 0)
• 16x sample rate using fractional baud rate generation (CTRLA.SAMPR = 1)
LIN frames start with a header transmitted by the master. The header consists of the break, sync, and
identifier fields. After the master transmits the header, the addressed slave will respond with 1-8 bytes of
data plus checksum.
SAM D5x/E5x Family Data Sheet
SERCOM USART - SERCOM Synchronous and Asyn...
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Datasheet
DS60001507E-page 933