HC705C9AGRSSLASHD datasheet(86/157 Pages) NXP

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General Release Speciﬁcation

Idle Line Wakeup

MC68HC705C9A — Rev. 2.0

Serial Communications Interface (SCI)

9.9 Idle Line Wakeup

In idle line wakeup mode, a dormant receiver wakes up as soon as the

RDI line becomes idle. Idle is defined as a continuous logic high level on

the RDI line for 10 (or 11) full bit times. Systems using this type of

wakeup must provide at least one character time of idle between

messages to wake up sleeping receivers, but must not allow any idle

time between characters within a message.

9.10 Address Mark Wakeup

In address mark wakeup, the most significant bit (MSB) in a character is

used to indicate whether it is an address (logic one) or data (logic zero)

character. Sleeping receivers will wake up whenever an address

character is received. Systems using this method for wakeup would set

the MSB of the first character of each message and leave it clear for all

other characters in the message. Idle periods may be present within

messages and no idle time is required between messages for this

wakeup method.

9.11 Receive Data In (RDI)

Receive data is the serial data that is applied through the input line and

the SCI to the internal bus. The receiver circuitry clocks the input at a

rate equal to 16 times the baud rate. This time is referred to as the RT

rate in Figure 9-4 and as the receiver clock in Figure 9-6.

The receiver clock generator is controlled by the baud rate register;

however, the SCI is synchronized by the start bit, independent of the

transmitter.

Once a valid start bit is detected, the start bit, each data bit, and the stop

bit are sampled three times at RT intervals 8 RT, 9 RT, and 10 RT (1 RT

is the position where the bit is expected to start), as shown in Figure 9-5.

The value of the bit is determined by voting logic which takes the value

of the majority of the samples. A noise flag is set when all three samples

on a valid start bit or data bit or the stop bit do not agree.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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