MMC2107 Datasheet, PDF (361/618 Pages) –

Freescale Semiconductor, Inc.
Serial Communications Interface Modules (SCI1 and SCI2)
Receiver
Figure 16-20 shows the effect of noise early in the start bit time.
Although this noise does not affect proper synchronization with the start
bit time, it does set the noise flag.
PERCEIVED AND ACTUAL START BIT
LSB
RXD
SAMPLES 1 1 1 1 1 1 1 1 1 0
1
0
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 16-20. Start Bit Search Example 4
Figure 16-21 shows a burst of noise near the beginning of the start bit
that resets the RT clock. The sample after the reset is low but is not
preceded by three high samples that would qualify as a falling edge.
Depending on the timing of the start bit search and on the data, the frame
may be missed entirely or it may set the framing error flag.
START BIT
LSB
RXD
NO START BIT FOUND
SAMPLES 1 1 1 1 1 1 1 1 1 0
0
1
100000000
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 16-21. Start Bit Search Example 5
MMC2107 – Rev. 2.0
MOTOROLA
Serial Communications Interface Modules (SCI1 and SCI2)
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Technical Data
361