Chapter 20 Serial Communication Interface (S12SCIV5)
MC9S12XE-Family Reference Manual Rev. 1.19
Freescale Semiconductor
751
In
, 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 20-24. Start Bit Search Example 3
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 20-25. 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
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