Datasheet

19.3.5 ISO 7816 Support
The UART offers basic support to allow communication with an ISO 7816 smartcard. When bit 3
(SMART) of the UARTCTL register is set, the UnTx signal is used as a bit clock, and the UnRx signal
is used as the half-duplex communication line connected to the smartcard. A GPIO signal can be
used to generate the reset signal to the smartcard. The remaining smartcard signals should be
provided by the system design. The maximum clock rate in this mode is system clock / 16.
When using ISO 7816 mode, the UARTLCRH register must be set to transmit 8-bit words (WLEN
bits 6:5 configured to 0x3) with EVEN parity (PEN set and EPS set). In this mode, the UART
automatically uses 2 stop bits, and the STP2 bit of the UARTLCRH register is ignored.
If a parity error is detected during transmission, UnRx is pulled Low during the second stop bit. In
this case, the UART aborts the transmission, flushes the transmit FIFO and discards any data it
contains, and raises a parity error interrupt, allowing software to detect the problem and initiate
retransmission of the affected data. Note that the UART does not support automatic retransmission
in this case.
19.3.6 Modem Handshake Support
This section describes how to configure and use the modem flow control and status signals for a
UART when connected as a DTE (data terminal equipment) or as a DCE (data communications
equipment). In general, a modem is a DCE and a computing device that connects to a modem is
the DTE.
19.3.6.1 Signaling
The status signals provided by a UART differ based on whether the UART is used as a DTE or
DCE. When used as a DTE, the modem flow control and status signals are defined as:
■ UnCTS is Clear To Send
■ UnDSR is Data Set Ready
■ UnDCD is Data Carrier Detect
■ UnRI is Ring Indicator
■ UnRTS is Request To Send
■ UnDTR is Data Terminal Ready
When used as a DCE, the modem flow control and status signals are defined as:
■ UnCTS is Request To Send
■ UnDSR is Data Terminal Ready
■ UnRTS is Clear To Send
■ UnDTR is Data Set Ready
Note that the support for DCE functions Data Carrier Detect and Ring Indicator are not provided. If
these signals are required, their function can be emulated by using a general-purpose I/O signal
and providing software support.
December 13, 20131316
Texas Instruments-Advance Information
Universal Asynchronous Receivers/Transmitters (UARTs)