Chapter 15 Serial Communication Interface (S12MC9S12XDP512V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 701
In Figure 15-24, a large burst of noise is perceived as the beginning of a start bit, although the test sampleat RT5 is high. The RT5 sample sets the noise flag. Although this is a worst-case misalignment of perceivedbit time, the data samples RT8, RT9, and RT10 are within the bit time and data recovery is successful.

Figure 15-24. Start Bit Search Example 3

Figure 15-25 shows the effect of noise early in the start bit time. Although this noise does not affect propersynchronization with the start bit time, it does set the noise flag.

Figure 15-25. 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