LM3S5D91 Datasheet, PDF (692/1340 Pages) Texas Instruments – Stellaris® LM3S5D91 Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
retransmission of the affected data. Note that the UART does not support automatic retransmission
in this case.
13.3.6
Modem Handshake Support
This section describes how to configure and use the modem flow control and status signals for
UART1 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.
13.3.6.1
Signaling
The status signals provided by UART1 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:
■ U1CTS is Clear To Send
■ U1DSR is Data Set Ready
■ U1DCD is Data Carrier Detect
■ U1RI is Ring Indicator
■ U1RTS is Request To Send
■ U1DTR is Data Terminal Ready
When used as a DCE, the the modem flow control and status signals are defined as:
■ U1CTS is Request To Send
■ U1DSR is Data Terminal Ready
■ U1RTS is Clear To Send
■ U1DTR 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.
13.3.6.2
Flow Control
Flow control can be accomplished by either hardware or software. The following sections describe
the different methods.
Hardware Flow Control (RTS/CTS)
Hardware flow control between two devices is accomplished by connecting the U1RTS output to the
Clear-To-Send input on the receiving device, and connecting the Request-To-Send output on the
receiving device to the U1CTS input.
The U1CTS input controls the transmitter. The transmitter may only transmit data when the U1CTS
input is asserted. The U1RTS output signal indicates the state of the receive FIFO. U1CTS remains
asserted until the preprogrammed watermark level is reached, indicating that the Receive FIFO has
no space to store additional characters.
692
January 22, 2012
Texas Instruments-Production Data