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

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SAM4S Series [DATASHEET]

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

 shows how the transmitter operates if hardware handshaking is enabled. The CTS pin disables the 

transmitter. If a character is being processing, the transmitter is disabled only after the completion of the current 

character and transmission of the next character happens as soon as the pin CTS falls.

The USART features an ISO7816-compatible operating mode. This mode permits interfacing with smart cards and 

Security Access Modules (SAM) communicating through an ISO7816 link. Both T = 0 and T = 1 protocols defined 

by the ISO7816 specification are supported.
Setting the USART in ISO7816 mode is performed by writing the USART_MODE field in US_MR to the value 0x4 

for protocol T = 0 and to the value 0x5 for protocol T = 1.

The ISO7816 is a half duplex communication on only one bidirectional line. The baud rate is determined by a 

division of the clock provided to the remote device (see “Baud Rate Generator” on page 761). 
The USART connects to a smart card as shown in 

. The TXD line becomes bidirectional and the baud 

rate generator feeds the ISO7816 clock on the SCK pin. As the TXD pin becomes bidirectional, its output remains 

driven by the output of the transmitter but only when the transmitter is active while its input is directed to the input 

of the receiver. The USART is considered as the master of the communication as it generates the clock. 

When operating in ISO7816, either in T = 0 or T = 1 modes, the character format is fixed. The configuration is 8 

data bits, even parity and 1 or 2 stop bits, regardless of the values programmed in the CHRL, MODE9, PAR and 

CHMODE fields. MSBF can be used to transmit LSB or MSB first. Parity Bit (PAR) can be used to transmit in 

normal or inverse mode. Refer to “USART Mode Register” on page 798 and “PAR: Parity Type” on page 799. 
The USART cannot operate concurrently in both receiver and transmitter modes as the communication is 

unidirectional at a time. It has to be configured according to the required mode by enabling or disabling either the 

RTS

RXBUFF

Write

US_CR

RXEN = 1

RXD

RXDIS = 1

CTS

TXD

Smart

Card

SCK

CLK

TXD

I/O

USART