Serial Communication Interface (S12SCIV5)
MC9S12XHY-Family Reference Manual, Rev. 1.01
484
Freescale Semiconductor
In
Figure 14-24
, 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 14-24. Start Bit Search Example 3
Figure 14-25
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 14-25. Start Bit Search Example 4
Reset RT Clock
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
5
RT
6
RT
7
RT
8
RT
9
R
T10
R
T13
R
T12
R
T11
R
T16
R
T15
R
T14
RT
4
RT
3
RT
2
RT
1
RT
5
RT
6
RT
7
RT
8
RT
9
Samples
RT Clock
RT Clock Count
Actual Start Bit
RXD
1
0
1
1
1
0
0
0
0
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
1
1
1
1
1
0
0
1
LSB
1
1
1
1
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