AT91SAM7S32-AI ATMEL [ATMEL Corporation], AT91SAM7S32-AI Datasheet - Page 283

• Manufacturer Part Number: AT91SAM7S32-AI
• Description: AT91 ARM Thumb-based Microcontrollers
• Manufacturer: ATMEL [ATMEL Corporation]

Figure 116. Receiver Behavior when Operating with Hardware Handshaking
Figure 117. Transmitter Behavior when Operating with Hardware Handshaking
ISO7816 Mode
ISO7816 Mode
Overview
Figure 118. Connection of a Smart Card to the USART
6071A–ATARM–28-Oct-04
RXBUFF
US_CR
Write
RXD
RTS
RXEN = 1
Figure 117 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 the
Mode Register (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 Genera-
tor” on page 269).
The USART connects to a smart card as shown in Figure 118. The TXD line becomes bidirec-
tional 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 pro-
grammed in the CHRL, MODE9, PAR and CHMODE fields. MSBF can be used to transmit
LSB or MSB first.
CTS
TXD
USART
SCK
TXD
CLK
I/O
AT91SAM7S32 Preliminary
Smart
Card
RXDIS = 1
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