Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Scheda Tecnica
Codici prodotto
AT91SAM9G25-EK
797
SAM9G25 [DATASHEET]
11032C–ATARM–25-Jan-13
39.7.3.15 Hardware Handshaking
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
the remote device, as shown in
.
Figure 39-27.Connection with a Remote Device for Hardware Handshaking
Setting the USART to operate with hardware handshaking is performed by writing the USART_MODE field in the Mode
Register (US_MR) to the value 0x2.
Register (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 DMAC channel for
reception. The transmitter can handle hardware handshaking in any case.
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 DMAC channel for
reception. The transmitter can handle hardware handshaking in any case.
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.
character and transmission of the next character happens as soon as the pin CTS falls.
Figure 39-28.Transmitter Behavior when Operating with Hardware Handshaking
39.7.4 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.
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 value 0x4 for protocol T = 0 and to the value 0x5 for protocol T = 1.
39.7.4.1 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
the clock provided to the remote device (see
).
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.
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.
USART
TXD
CTS
Remote
Device
RXD
TXD
RXD
RTS
RTS
CTS
CTS
TXD