Figure 818. Start Detection And Sampling For Over Sampling Rate = 4 (Case 1) - STMicroelectronics SPC572L series Reference Manual

RM0400

Figure 818. Start detection and sampling for over sampling rate = 4 (Case 1)

1:1 voting, CSP = 3
(Third sample point considered)
1
–
Sample count
Note:
1) D , D : Databits
0 1
2) X: Due to sampling during transition of the bit, value might be sampled as a '0' or '1' depending on the rise/fall time.
Therefore 'X' refers to a indeterministic value.
Figure 819. Start detection and sampling for over sampling rate = 4 (Case 2a)
1:1 voting, CSP = 3
1
–
Sample count
Note:
1) D , D : Databits
0 1
2) X: Due to sampling during transition of the bit, value might be sampled as a '0' or '1' depending on the rise/fall time.
Therefore 'X' refers to a indeterministic value.
The choice of the correct sample points depends on the external Rx signal quality. During
the application development process, the error information indicated by the parity error can
help to find the best setting for an application-specific hardware signal.
To sample at the correct point therefore, CSP has to be changed to two; resulting in the
following situation:
1 1 1 1 1 1
– – – – – –
1 1 1 1 1 1
– – – – – –
DocID027809 Rev 4
Start bit Data bit 0
0 0 0 X D D
0
0 1
0 1 2 3
Start detected
Start bit Data bit 0
X 0 0 0 D D
0
3 0
– 0 1 2
Start detected
Data bit 1
D D D D D
0 0 0 1 1 1
0 1 2
2 3
Data being sampled is corected
Data bit 1
D D D D D
0 0 0 1 1 1
3 0 1
1 2
Last point of data sampled due to
incorrect start detection
LINFlexD
D ........
1
3
D ........
1
2 3
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