MMC2107 Datasheet, PDF (362/618 Pages) –

Freescale Semiconductor, Inc.
Serial Communications Interface Modules (SCI1 and SCI2)
In Figure 16-22 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.
START BIT
LSB
RXD
SAMPLES 1 1 1 1 1 1 1 1 1 0
0
0
0101
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 16-22. Start Bit Search Example 6
16.12.4 Framing Errors
If the data recovery logic does not detect a 1 where the stop bit should
be in an incoming frame, it sets the FE flag in SCISR1. A break frame
also sets the FE flag because a break frame has no stop bit. The FE flag
is set at the same time that the RDRF flag is set.
16.12.5 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 RT8, RT9, and RT10 stop bit data samples to fall outside the
stop bit. A noise error occurs if the samples are not all the same value.
If more than one of the samples is outside the stop bit, a framing error
occurs. In most applications, the baud rate tolerance is much more than
the degree of misalignment that is likely to occur.
As the receiver samples an incoming frame, it resynchronizes the RT
clock on any valid falling edge within the frame. Resynchronization
within frames corrects misalignments between transmitter bit times and
receiver bit times.
Technical Data
362
Serial Communications Interface Modules (SCI1 and SCI2)
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MMC2107 – Rev. 2.0
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