HC705C9AGRSSLASHD datasheet(85/157 Pages) NXP

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General Release Specification

Receiver Wakeup Operation

MC68HC705C9A — Rev. 2.0

Serial Communications Interface (SCI)

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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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