MC68HC705C9A_1 Datasheet, PDF (85/157 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
General Release Specification
Receiver Wakeup Operation
9.8 Receiver Wakeup Operation
The receiver logic hardware also supports a receiver wakeup function
which is intended for systems having more than one receiver. With this
function a transmitting device directs messages to an individual receiver
or group of receivers by passing addressing information as the initial
byte(s) of each message. The wakeup function allows receivers not
addressed to remain in a dormant state for the remainder of the
unwanted message. This eliminates any further software overhead to
service the remaining characters of the unwanted message and thus
improves system performance.
The receiver is placed in wakeup mode by setting the receiver wakeup
bit (RWU) in the SCCR2 register. While RWU is set, all of the
receiver-related status flags (RDRF, IDLE, OR, NF, and FE) are
inhibited (cannot become set).
NOTE:
The idle line detect function is inhibited while the RWU bit is set.
Although RWU may be cleared by a software write to SCCR2, it would
be unusual to do so.
Normally, RWU is set by software and is cleared automatically in
hardware by one of these methods: idle line wakeup or address mark
wakeup.
MC68HC705C9A — Rev. 2.0
Serial Communications Interface (SCI)
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