SAM4L Datasheet, PDF (589/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
24.6.8.7
Transmit Character Repetition
The USART can be configured to automatically re-send a character if it receives a NACK. Writ-
ing a non-zero value to MR.MAX_ITERATION will enable and determine the number of
consecutive re-transmissions. If the number of unsuccessful re-transmissions equals
MAX_ITERATION, the iteration bit (CSR.ITER) is set. An interrupt request is generated if the
ITER bit in the Interrupt Mask Register (IMR.ITER) is set. Writing a one to the Reset Iteration bit
(CR.RSTIT) will clear CSR.ITER.
24.6.8.8
Disable Successive Receive NACK
The receiver can limit the number of consecutive NACKs to the value in MR.MAX_ITERATION.
This is enabled by writing a one to the Disable Successive NACK bit (MR.DSNACK). If the num-
ber of NACKs is about to exceed MR.MAX_ITERATION, the character will instead be accepted
as valid and CSR.ITER is set.
24.6.9
IrDA Mode
The USART features an IrDA mode, supporting asynchronous, half-duplex, point-to-point wire-
less communication. It embeds the modulator and demodulator, allowing for a glueless
connection to the infrared transceivers, as shown in Figure 24-24. The IrDA mode is enabled by
writing 0x8 to MR.MODE. This activates the IrDA specification v1.1 compliant modem. Data
transfer speeds ranging from 2.4Kbit/s to 115.2Kbit/s are supported and the character format is
fixed to one start bit, eight data bits, and one stop bit.
Figure 24-24. Connection to IrDA Transceivers
USART
Receiver
Demodulator _RXD
Transmitter
Modulator
TXD
IrDA
Transceivers
RX
TX
The receiver and the transmitter must be exclusively enabled or disabled, according to the direc-
tion of the transmission. To receive IrDA signals, the following needs to be done:
• Disable TX and enable RX.
• Configure the TXD pin as an I/O, outputting zero to avoid LED activation. Disable the internal
pull-up for improved power consumption.
• Receive data.
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