Datasheet

Serial Communications Interface (SCI)
Functional Description
MC9S12DP256 — Revision 1.1
Serial Communications Interface (SCI)
In Figure 74, a noise burst makes the majority of data samples RT8,
RT9, and RT10 high. This sets the noise flag but does not reset the RT
clock. In start bits only, the RT8, RT9, and RT10 data samples are
ignored.
Figure 74 Start Bit Search Example 6
Framing Errors If the data recovery logic does not detect a logic 1 where the stop bit
should be in an incoming frame, it sets the framing error flag, FE, in SCI
status register 1 (SCISR1). A break character also sets the FE flag
because a break character has no stop bit. The FE flag is set at the same
time that the RDRF flag is set.
Baud Rate
Tolerance
A transmitting device may be operating at a baud rate below or above
the receiver baud rate. Accumulated bit time misalignment can cause
one of the three stop bit data samples (RT8, RT9, and RT10) to fall
outside the actual stop bit. A noise error will occur if the RT8, RT9, and
RT10 samples are not all the same logical values. A framing error will
occur if the receiver clock is misaligned in such a way that the majority
of the RT8, RT9, and RT10 stop bit samples are a logic zero.
As the receiver samples an incoming frame, it re-synchronizes the RT
clock on any valid falling edge within the frame. Resynchronization
within frames will correct a misalignment between transmitter bit times
and receiver bit times.
RESET RT CLOCK
RT1 RT1 RT1 RT1 RT1 RT1 RT1 RT1 RT1 RT1 RT2 RT3 RT4 RT7 RT6 RT5
RT10
RT9 RT8
RT14 RT13 RT12 RT11 RT15 RT16
RT1 RT2 RT3
SAMPLES
RT CLOCK
RT CLOCK COUNT
START BIT
sci_rx_ind
11111000
LSB
11 1 1 0 110
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
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