Datasheet

Chapter 8 Serial Communication Interface (SCIV3)
MC9S12E128 Data Sheet, Rev. 1.07
Freescale Semiconductor 269
In Figure 8-18, a large burst of noise is perceived as the beginning of a start bit, although the test sample
at RT5 is high. The RT5 sample sets the noise flag. Although this is a worst-case misalignment of
perceived bit time, the data samples RT8, RT9, and RT10 are within the bit time and data recovery is
successful.
Figure 8-18. Start Bit Search Example 3
Figure 8-19 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.
Figure 8-19. Start Bit Search Example 4
RESET RT CLOCK
RT1 RT1 RT1 RT1 RT2 RT3 RT4 RT5 RT6 RT7 RT8 RT9
RT10 RT13 RT12 RT11 RT16 RT15 RT14
RT4 RT3 RT2 RT1 RT5 RT6 RT7 RT8 RT9
SAMPLES
RT CLOCK
RT CLOCK COUNT
ACTUAL START BIT
RXD
101110000
LSB
0
PERCEIVED START BIT
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
PERCEIVED AND ACTUAL START BIT
RXD
11111001
LSB
11 1 1