40.3.3.2 Receiver wakeup operation
Receiver wakeup is a hardware mechanism that allows an UART receiver to ignore the
characters in a message intended for a different UART receiver. In such a system, all
receivers evaluate the first character(s) of each message, and as soon as they determine
the message is intended for a different receiver, they write logic 1 to the receiver wake up
control bit(UART_C2[RWU]). When RWU bit is set, the status flags associated with the
receiver, with the exception of the idle bit, IDLE, when UART_S2[RWUID] bit is set,
are inhibited from setting, thus eliminating the software overhead for handling the
unimportant message characters. At the end of a message, or at the beginning of the next
message, all receivers automatically force UART_C2[RWU] to 0 so all receivers wake
up in time to look at the first character(s) of the next message.
40.3.3.2.1 Idle-line wakeup
When wake is cleared, the receiver is configured for idle-line wakeup. In this mode,
UART_C2[RWU] is cleared automatically when the receiver detects a full character time
of the idle-line level. The UART_C1[M] control bit selects 8-bit or 9-bit data mode and
the UART_BDH[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 or 11 or 12 bit
times because of the start and stop bits.
When UARTI_C2[RWU] is one and UART_S2[RWUID] is zero, the idle condition that
wakes up the receiver does not set the UART_S1[IDLE] flag. The receiver wakes up and
waits for the first data character of the next message that sets the UART_S1[RDRF] flag
and generates an interrupt if enabled. When UART_S2[RWUID] is one, any idle
condition sets the UART_S1[IDLE] flag and generates an interrupt if enabled, regardless
of whether UART_C2[RWU] is zero or one.
The idle-line type (UART_C1[ILT]) control bit selects one of two ways to detect an idle
line. When UART_C1[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 UART_C1[ILT] is set, the idle bit counter does not start until after a stop bit
time, so the idle detection is not affected by the data in the last character of the previous
message.
40.3.3.2.2 Address-mark wakeup
When wake is set, the receiver is configured for address-mark wakeup. In this mode,
UART_C2[RWU] is cleared automatically when the receiver detects a, or two, if
UART_BDH[SBNS] = 1, logic 1 in the most significant bits of a received character,
eighth bit when UART_C1[M] is cleared and ninth bit when UART_C1[M] is set.
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
766 Freescale Semiconductor, Inc.
To Next Page
Loading...
