Atmel SAM4L-EK Atmel ATSAM4L-EK ATSAM4L-EK Data Sheet

42023E–SAM–07/2013

In order to use this module, other parts of the system must be configured correctly, as described
below.

The USART pins may be multiplexed with the I/O Controller lines. The user must first configure
the I/O Controller to assign these pins to their peripheral functions. Unused I/O lines may be
used for other purposes.

To prevent the TXD line from falling when the USART is disabled, the use of an internal pull-up
is required. If the hardware handshaking feature or modem mode is used, the internal pull-up on
RTS must also be enabled.

All the pins of the modems may or may not be implemented on the USART. On USARTs not
equipped with the corresponding pins, the associated control bits and statuses have no effect on
the behavior of the USART.

The clock for the USART bus interface (CLK_USART) is generated by the Power Manager. It is
recommended to disable the USART before disabling the clock, to avoid freezing the USART in
an undefined state.

The USART interrupt request line is connected to the NVIC. Using the USART interrupt requires
the NVIC to be programmed first.

I/O Lines Description

CLK

Serial Clock

I/O

TXD

Transmit Serial Data

or Master Out Slave In (MOSI) in SPI master mode

or Master In Slave Out (MISO) in SPI slave mode

Output

RXD

Receive Serial Data

or Master In Slave Out (MISO) in SPI master mode

or Master Out Slave In (MOSI) in SPI slave mode

Input

RI

Ring Indicator

Input

Low

DSR

Data Set Ready

Input

Low

DCD

Data Carrier Detect

Input

Low

DTR

Data Terminal Ready 

Output

Low

CTS

Clear to Send

or Slave Select (NSS) in SPI slave mode

Input

Low

RTS

Request to Send

or Slave Select (NSS) in SPI master mode

Output

Low