Note
The RT8, RT9, and RT10 samples do not affect start bit
verification. If any or all of the RT8, RT9, and RT10 start bit
samples are logic 1s following a successful start bit verification,
the noise flag (S1[NF]) is set and the receiver assumes that the
bit is a start bit (logic 0).
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and
RT10. The following table summarizes the results of the stop bit samples.
Table 46-73. Stop bit recovery
RT8, RT9, and RT10 samples
Framing error flag
Noise flag
000
1
0
001
1
1
010
1
1
011
0
1
100
1
1
101
0
1
110
0
1
111
0
0
In the following figure, the verification samples RT3 and RT5 determine that the first low
detected was noise and not the beginning of a start bit. The RT clock is reset and the start
bit search begins again. The noise flag is not set because the noise occurred before the
start bit was found.
SAMPLES
Rx pin input
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
1
1
1
0
1
0
0
0
START BIT
LSB
R
T1
R
T1
R
T1
R
T1
R
T2
R
T4
R
T3
R
T5
R
T1
R
T1
R
T2
R
T3
R
T1
0
R
T1
R
T2
R
T3
1
1
0
0
0
0
R
T1
1
R
T1
2
R
T1
3
R
T1
4
R
T1
5
R
T1
6
R
T4
R
T5
R
T6
R
T7
R
T8
R
T9
Figure 46-68. Start bit search example 1
In the following figure, verification sample at RT3 is high. The RT3 sample sets the noise
flag. Although the perceived bit time is misaligned, the data samples RT8, RT9, and
RT10 are within the bit time and data recovery is successful.
Functional description
KV4x Reference Manual, Rev. 2, 02/2015
1304
Preliminary
Freescale Semiconductor, Inc.
Содержание freescale KV4 Series
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