Chapter 20 Serial Communication Interface (S12SCIV5)
MC9S12XE-Family Reference Manual , Rev. 1.19
750
Freescale Semiconductor
In
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.
Figure 20-22. Start Bit Search Example 1
In
, 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.
Figure 20-23. Start Bit Search Example 2
Reset RT Clock
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
5
RT
1
RT
1
RT
2
RT
3
RT
4
RT
7
RT
6
RT
5
R
T10
RT
9
RT
8
R
T14
R
T13
R
T12
R
T11
R
T15
R
T16
RT
1
RT
2
RT
3
Samples
RT Clock
RT Clock Count
Start Bit
RXD
1
1
0
1
1
1
1
0
0
0
0
0
LSB
0
0
Reset RT Clock
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
5
RT
6
RT
7
RT
8
R
T11
R
T10
RT
9
R
T14
R
T13
R
T12
RT
2
RT
1
R
T16
R
T15
RT
3
RT
4
RT
5
RT
6
RT
7
Samples
RT Clock
RT Clock Count
Actual Start Bit
RXD
1
1
1
1
1
1
0
0
0
0
LSB
0
0
Perceived Start Bit
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages