Receiver
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
20-13
To verify the start bit and to detect noise, data sampling logic takes samples at RT3 and RT5. If
both samples are logic 1 the RT counter is reset and a new search for a start bit begins, else also
RT7 sample is taken. If at least two samples (from RT3, RT5, and RT7) are logic 0 then the start
bit is perceived. The noise flag, NF, is set if two samples are logic 0 and one is logic 1. Table
20-4 summarizes the results of the start bit verification samples.
If start bit verification is not successful, the RT counter is reset and a new search for a start bit
begins. To determine the value of a data bit and to detect noise, sample logic takes samples at
RT8, RT9, and RT10. The data bit value is determined by the majority of the samples. The noise
flag, NF, is set if not all samples have the same logical value. Table 20-5 summarizes the results
of the data bit samples.
Figure 20-9. Receiver Data Sampling
Table 20-4. Start Bit Verification
RT3, RT5, and RT7 Samples
Start Bit Verification
Noise Flag
000
Yes
0
001
Yes
1
010
Yes
1
011
No
0
100
Yes
1
101
No
0
11
(RT7 sample is not taken)
No
0
Table 20-5. Data Bit Recovery
RT8, RT9, and RT10 Samples
Data Bit Determination
Noise Flag
000
0
0
001
0
1
010
0
1
011
1
1
100
0
1
101
1
1
110
1
1
111
1
0
Reset RT Clock
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
5
RT
8
RT
7
RT
6
RT1
1
RT1
0
RT
9
RT1
5
RT1
4
RT1
3
RT1
2
RT1
6
RT
1
RT
2
RT
3
RT
4
Samples
RT Clock
RT Clock Count
Start Bit
URXD
Start Bit
Qualification
Start Bit
Data
Sampling
1
1
1
1
1
1
1
1 0
0
0
0
0
0
0
LSB
Verification
Содержание MSC8144E
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