NXP Semiconductors K32 L2A Series, Reference Manual, Page: 849 / 1379

31.3.5.1 Infrared transmit encoder
The infrared transmit encoder converts serial bits of data from transmit shift register to
the LPUART_TX signal. A narrow pulse is transmitted for a zero bit and no pulse for a
one bit. The narrow pulse is sent at the start of the bit with a duration of 1/OSR, 2/OSR,
3/OSR, or 4/OSR of a bit time. A narrow low pulse is transmitted for a zero bit when
LPUART_CTRL[TXINV] is cleared, while a narrow high pulse is transmitted for a zero
bit when LPUART_CTRL[TXINV] is set.
31.3.5.2 Infrared receive decoder
The infrared receive block converts data from the LPUART_RX signal to the receive
shift register. A narrow pulse is expected for each zero received and no pulse is expected
for each one received. A narrow low pulse is expected for a zero bit when
LPUART_STAT[RXINV] is cleared, while a narrow high pulse is expected for a zero bit
when LPUART_STAT[RXINV] is set. This receive decoder meets the edge jitter
requirement as defined by the IrDA serial infrared physical layer specification.
31.3.6 Interrupts and status flags
The LPUART transmitter has two status flags that can optionally generate hardware
interrupt requests. Transmit data register empty LPUART_STAT[TDRE]) indicates when
there is room in the transmit data buffer to write another transmit character to
LPUART_DATA. If the transmit interrupt enable LPUART_CTRL[TIE]) bit is set, a
hardware interrupt is requested when LPUART_STAT[TDRE] is set. Transmit complete
(LPUART_STAT[TC]) indicates that the transmitter is finished transmitting all data,
preamble, and break characters and is idle with LPUART_TX at the inactive level. This
flag is often used in systems with modems to determine when it is safe to turn off the
modem. If the transmit complete interrupt enable (LPUART_CTRL[TCIE]) bit is set, a
hardware interrupt is requested when LPUART_STAT[TC] is set. Instead of hardware
interrupts, software polling may be used to monitor the LPUART_STAT[TDRE] and
LPUART_STAT[TC] status flags if the corresponding LPUART_CTRL[TIE] or
LPUART_CTRL[TCIE] local interrupt masks are cleared.
When a program detects that the receive data register is full (LPUART_STAT[RDRF] =
1), it gets the data from the receive data register by reading LPUART_DATA. The
LPUART_STAT[RDRF] flag is cleared by reading LPUART_DATA.
Chapter 31 Low Power Universal Asynchronous Receiver/Transmitter (LPUART)
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors 849