bit in UARTCTL. The parity bit is then checked if parity mode is enabled. Data length and parity are
defined in the UARTLCRH register.
Lastly, a valid stop bit is confirmed if the UnRxsignal is High, otherwise a framing error has occurred.
When a full word is received, the data is stored in the receive FIFO along with any error bits
associated with that word.
13.3.4 Serial IR (SIR)
The UART peripheral includes an IrDA serial-IR (SIR) encoder/decoder block. The IrDA SIR block
provides functionality that converts between an asynchronous UART data stream and a half-duplex
serial SIR interface. No analog processing is performed on-chip. The role of the SIR block is to
provide a digital encoded output and decoded input to the UART. When enabled, the SIR block
uses the UnTxand UnRx pins for the SIR protocol. These signals should be connected to an infrared
transceiver to implement an IrDA SIR physical layer link. The SIR block can receive and transmit,
but it is only half-duplex so it cannot do both at the same time. Transmission must be stopped before
data can be received. The IrDA SIR physical layer specifies a minimum 10-ms delay between
transmission and reception.The SIR block has two modes of operation:
■ In normal IrDA mode, a zero logic level is transmitted as a high pulse of 3/16th duration of the
selected baud rate bit period on the output pin, while logic one levels are transmitted as a static
LOW signal. These levels control the driver of an infrared transmitter, sending a pulse of light
for each zero. On the reception side, the incoming light pulses energize the photo transistor base
of the receiver, pulling its output LOW and driving the UART input pin LOW.
■ In low-power IrDA mode, the width of the transmitted infrared pulse is set to three times the
period of the internally generated IrLPBaud16 signal (1.63 µs, assuming a nominal 1.8432 MHz
frequency) by changing the appropriate bit in the UARTCR register. See page 636 for more
information on IrDA low-power pulse-duration configuration.
Figure 13-3 on page 619 shows the UART transmit and receive signals, with and without IrDA
modulation.
Figure 13-3. IrDA Data Modulation
1
0
10
0
0
1
1
0
1
Data bits
1
0
10
0
0
1
1
0
1
Data bits
Start
bit
Start Stop
Bit period
Bit period
3
16
UnTx
UnTx with IrDA
UnRx with IrDA
UnRx
Stop
bit
In both normal and low-power IrDA modes:
■ During transmission, the UART data bit is used as the base for encoding
■ During reception, the decoded bits are transferred to the UART receive logic
619July 24, 2012
Texas Instruments-Production Data
Stellaris
®
LM3S6G65 Microcontroller
OBSOLETE: TI has discontinued production of this device.
