Information

45.4.3.9.1 Idle input line wakeup (C1[WAKE] = 0)
In this wakeup method, an idle condition on the unsynchronized receiver input signal
clears C2[RWU] and wakes the UART. The initial frame or frames of every message
contain addressing information. All receivers evaluate the addressing information, and
receivers for which the message is addressed process the frames that follow. Any receiver
for which a message is not addressed can set its C2[RWU] and return to the standby state.
C2[RWU] remains set and the receiver remains in standby until another idle character
appears on the unsynchronized receiver input signal.
Idle line wakeup requires that messages be separated by at least one idle character and
that no message contains idle characters.
When C2[RWU] is 1 and S2[RWUID] is 0, the idle character that wakes the receiver
does not set S1[IDLE] or the receive data register full flag, S1[RDRF]. The receiver
wakes and waits for the first data character of the next message which is stored in the
receive data buffer. When S2[RWUID] and C2[RWU] are set and C1[WAKE] is cleared,
any idle condition sets S1[IDLE] and generates an interrupt if enabled.
Idle input line wakeup is not supported when C7816[ISO_7816E] is set/enabled.
45.4.3.9.2 Address mark wakeup (C1[WAKE] = 1)
In this wakeup method, a logic 1 in the bit position immediately preceding the stop bit of
a frame clears C2[RWU] and wakes the UART. A logic 1 in the bit position immediately
preceeding the stop bit marks a frame as an address frame that contains addressing
information. All receivers evaluate the addressing information, and the receivers for
which the message is addressed process the frames that follow. Any receiver for which a
message is not addressed can set its C2[RWU] and return to the standby state. C2[RWU]
remains set and the receiver remains in standby until another address frame appears on
the unsynchronized receiver input signal.
A logic 1 in the bit position immediately preceding the stop bit clears the receiver's
C2[RWU] before the stop bit is received and places the received data into the receiver
data buffer.
Address mark wakeup allows messages to contain idle characters but requires that the bit
position immediately preceding the stop bit be reserved for use in address frames.
If module is in standby mode and nothing triggers to wake the UART, no error flag is set
even if an invalid error condition is detected on the receiving data line.
Address mark wakeup is not supported when C7816[ISO_7816E] is set/enabled.
Chapter 45 Universal Asynchronous Receiver/Transmitter (UART)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 1119