Datasheet

531
SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
Figure 33-18 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.
Figure 33-18. Receiver Behavior when Operating with Hardware Handshaking
Figure 33-19 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.
Figure 33-19. Transmitter Behavior when Operating with Hardware Handshaking
33.6.4 ISO7816 Mode
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 the Mode Register
(US_MR) to the value 0x4 for protocol T = 0 and to the value 0x5 for protocol T = 1.
33.6.4.1 ISO7816 Mode Overview
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 516).
The USART connects to a smart card as shown in Figure 33-20. 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.
Figure 33-20. Connection of a Smart Card to the USART
RTS
RXBUFF
Write
US_CR
RXEN = 1
RXD
RXDIS = 1
CTS
TXD
Smart
Card
SCK
CLK
TXD
I/O
USART