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37.4.3.2.1 Idle-line wakeup
When wake is cleared, the receiver is configured for idle-line wakeup. In this mode,
LPUART_CTRL[RWU] is cleared automatically when the receiver detects a full
character time of the idle-line level. The LPUART_CTRL[M] and
LPUART_BAUD[M10] control bit selects 8-bit to 10-bit data mode and the
LPUART_BAUD[SBNS] bit selects 1-bit or 2-bit stop bit number that determines how
many bit times of idle are needed to constitute a full character time, 10 to 13 bit times
because of the start and stop bits.
When LPUART_CTRL[RWU] is one and LPUART_STAT[RWUID] is zero, the idle
condition that wakes up the receiver does not set the LPUART_STAT[IDLE] flag. The
receiver wakes up and waits for the first data character of the next message that sets the
LPUART_STAT[RDRF] flag and generates an interrupt if enabled. When
LPUART_STAT[RWUID] is one, any idle condition sets the LPUART_STAT[IDLE]
flag and generates an interrupt if enabled, regardless of whether LPUART_CTRL[RWU]
is zero or one.
The idle-line type (LPUART_CTRL[ILT]) control bit selects one of two ways to detect
an idle line. When LPUART_CTRL[ILT] is cleared, the idle bit counter starts after the
start bit so the stop bit and any logic 1s at the end of a character count toward the full
character time of idle. When LPUART_CTRL[ILT] is set, the idle bit counter does not
start until after the stop bit time, so the idle detection is not affected by the data in the last
character of the previous message.
37.4.3.2.2 Address-mark wakeup
When LPUART_CTRL[WAKE] is set, the receiver is configured for address-mark
wakeup. In this mode, LPUART_CTRL[RWU] is cleared automatically when the
receiver detects a logic 1 in the most significant bit of a received character.
Address-mark wakeup allows messages to contain idle characters, but requires the MSB
be reserved for use in address frames. The logic 1 in the MSB of an address frame clears
the LPUART_CTRL[RWU] bit before the stop bits are received and sets the
LPUART_STAT[RDRF] flag. In this case, the character with the MSB set is received
even though the receiver was sleeping during most of this character time.
Chapter 37 Low Power Universal asynchronous receiver/transmitter (LPUART)
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.
671