Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

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The receiver detects a break condition when all data, parity and stop bits are low. This corresponds to detecting a 

framing error with data to 0x00, but FRAME remains low. 
When the low stop bit is detected, the receiver asserts the RXBRK bit in US_CSR. This bit may be cleared by 

writing US_CR with the bit RSTSTA to 1.
An end of receive break is detected by a high level for at least 2/16 of a bit period in asynchronous operating mode 

or one sample at high level in synchronous operating mode. The end of break detection also asserts the RXBRK 

bit.

The USART features a hardware handshaking out-of-band flow control. The RTS and CTS pins are used to 

connect with the remote device, as shown in 

Setting the USART to operate with hardware handshaking is performed by writing the USART_MODE field in 

US_MR to the value 0x2. 
The USART behavior when hardware handshaking is enabled is the same as the behavior in standard 

synchronous or asynchronous mode, except that the receiver drives the RTS pin as described below and the level 

on the CTS pin modifies the behavior of the transmitter as described below. Using this mode requires using the 

PDC channel for reception. The transmitter can handle hardware handshaking in any case.

 shows how the receiver operates if hardware handshaking is enabled. The RTS pin is driven high if 

the receiver is disabled and if the status RXBUFF (Receive Buffer Full) coming from the PDC channel is high. 

Normally, the remote device does not start transmitting while its CTS pin (driven by RTS) is high. As soon as the 

receiver is enabled, the RTS falls, indicating to the remote device that it can start transmitting. Defining a new 

buffer to the PDC clears the status bit RXBUFF and, as a result, asserts the pin RTS low.

D0

D1

D2

D3

D4

D5

D6

D7

TXD

Start 

Bit

Parity

Bit

Stop

Bit

Baud Rate

 Clock

Write

US_CR

TXRDY

TXEMPTY

STPBRK = 1

STTBRK = 1 

Break Transmission

End of Break

USART

TXD

CTS

Remote 

Device

RXD

TXD

RXD

RTS

RTS

CTS