Datasheet

Figure 26-9. Transmitter Behavior when Operating with Hardware Handshaking
CTS
TXD
26.6.3.3 IrDA Modulation and Demodulation
Transmission and reception can be encoded IrDA compliant up to 115.2 kb/s. IrDA modulation and
demodulation work in the following configuration:
IrDA encoding enabled (CTRLB.ENC=1),
Asynchronous mode (CTRLA.CMODE=0),
and 16x sample rate (CTRLA.SAMPR[0]=0).
During transmission, each low bit is transmitted as a high pulse. The pulse width is 3/16 of the baud rate
period, as illustrated in the figure below.
Figure 26-10. IrDA Transmit Encoding
IrDA encoded TXD
TXD
1 baud clock
3/16 baud clock
The reception decoder has two main functions.
The first is to synchronize the incoming data to the IrDA baud rate counter. Synchronization is performed
at the start of each zero pulse.
The second main function is to decode incoming Rx data. If a pulse width meets the minimum length set
by configuration (RXPL.RXPL), it is accepted. When the baud rate counter reaches its middle value (1/2
bit length), it is transferred to the receiver.
Note:  Note that the polarity of the transmitter and receiver are opposite: During transmission, a '0' bit is
transmitted as a '1' pulse. During reception, an accepted '0' pulse is received as a '0' bit.
Example: The figure below illustrates reception where RXPL.RXPL is set to 19. This
indicates that the pulse width should be at least 20 SE clock cycles. When using
BAUD=0xE666 or 160 SE cycles per bit, this corresponds to 2/16 baud clock as
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 26-11. IrDA Receive Decoding
IrDA encoded RXD
RXD
Baud clock
20 SE clock cycles
0 0.5
1
1.5
2 2.5
26.6.3.4 Break Character Detection and Auto-Baud
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),
SAM D21 Family
SERCOM USART
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Datasheet Complete
DS40001882D-page 478