TM4C123GH6ZXR Datasheet, PDF (930/1472 Pages) Texas Instruments – Tiva Microcontroller

Universal Asynchronous Receivers/Transmitters (UARTs)
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 UARTCTL register (see page 952).
Whether the device is in normal or low-power IrDA mode, a start bit is deemed valid if the decoder
is still Low, one period of IrLPBaud16 after the Low was first detected. This enables a normal-mode
UART to receive data from a low-power mode UART that can transmit pulses as small as 1.41 µs.
Thus, for both low-power and normal mode operation, the ILPDVSR field in the UARTILPR register
must be programmed such that 1.42 MHz < F_IrLPBaud16 < 2.12 MHz, resulting in a low-power pulse
duration of 1.41–2.11 μs (three times the period of IrLPBaud16). The minimum frequency of
IrLPBaud16 ensures that pulses less than one period of IrLPBaud16 are rejected, but pulses
greater than 1.4 μs are accepted as valid pulses.
Figure 14-3 on page 930 shows the UART transmit and receive signals, with and without IrDA
modulation.
Figure 14-3. IrDA Data Modulation
UnTx
Start
bit
0
1
Data bits
0
1
0
0
1
1
Stop
bit
0
1
UnTx with IrDA
UnRx with IrDA
Bit period
3
16
Bit period
UnRx
0
1
Start
0
1
0
0
Data bits
1
1
0
1
Stop
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
The IrDA SIR physical layer specifies a half-duplex communication link, with a minimum 10-ms
delay between transmission and reception. This delay must be generated by software because it
is not automatically supported by the UART. The delay is required because the infrared receiver
electronics might become biased or even saturated from the optical power coupled from the adjacent
transmitter LED. This delay is known as latency or receiver setup time.
930
June 12, 2014
Texas Instruments-Production Data