MC68HC705C9A_1 Datasheet, PDF (86/157 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
General Release Specification _{Idle Line Wakeup}
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.
MC68HC705C9A — Rev. 2.0
Serial Communications Interface (SCI)
For More Information On This Product,
Go to: www.freescale.com