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25.6.2.3 Clock Generation – Baud-Rate Generator
25.6.2.3.1 Asynchronous Arithmetic Mode BAUD Value Selection
26.6.3 Additional Features
26.6.3.1 Parity
Even or odd parity can be selected for error checking by writing 0x1 to the Frame Format bit field in the
Control A register (CTRLA.FORM).
If even parity is selected (CTRLB.PMODE=0), the parity bit of an outgoing frame is '1' if the data contains
an odd number of bits that are '1', making the total number of '1' even.
If odd parity is selected (CTRLB.PMODE=1), the parity bit of an outgoing frame is '1' if the data contains
an even number of bits that are '0', making the total number of '1' odd.
When parity checking is enabled, the parity checker calculates the parity of the data bits in incoming
frames and compares the result with the parity bit of the corresponding frame. If a parity error is detected,
the Parity Error bit in the Status register (STATUS.PERR) is set.
26.6.3.2 Hardware Handshaking
The USART features an out-of-band hardware handshaking flow control mechanism, implemented by
connecting the RTS and CTS pins with the remote device, as shown in the figure below.
Figure 26-7. Connection with a Remote Device for Hardware Handshaking
RXD
CTS
RTS
USART
TXD
RTS
CTS
Remote
Device
TXD
RXD
Hardware handshaking is only available in the following configuration:
• USART with internal clock (CTRLA.MODE=1),
• Asynchronous mode (CTRLA.CMODE=0),
• and Flow control pinout (CTRLA.TXPO=2).
When the receiver is disabled or the receive FIFO is full, the receiver will drive the RTS pin high. This
notifies the remote device to stop transfer after the ongoing transmission. Enabling and disabling the
receiver by writing to CTRLB.RXEN will set/clear the RTS pin after a synchronization delay. When the
receive FIFO goes full, RTS will be set immediately and the frame being received will be stored in the
shift register until the receive FIFO is no longer full.
Figure 26-8. Receiver Behavior when Operating with Hardware Handshaking
RTS
Rx FIFO Full
RXD
RXEN
The current CTS Status is in the STATUS register (STATUS.CTS). Character transmission will start only if
STATUS.CTS=0. When CTS is set, the transmitter will complete the ongoing transmission and stop
transmitting.
SAM D21 Family
SERCOM USART
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 477