NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
7-bit random number
S0
S1
S2
S3
S4
S5
S6
S
D
Q
D
Q
D
Q
D
Q
D
Q
D
Q
D Q
R
R
R
R
R
R
CLK
RFMRST
Galois primitive polynomial = X7 + X3 + 1
aaa-028034
Figure 41.ꢀLFSR implementation
A value of all zeros in the LFSR will remain unchanged with every clock input and cannot
be used as a starting "seed."
The resulting range of times for the initial and interframe pseudo-random time will be
as given in Table 131 for both the design center and the variation resulting from the
tolerance of the MFO clock.
Table 131.ꢀRandomization interval times
Time Interval Including MFO Tolerance (ms)
Time
Randomization
Number
Ideal Time Interval (ms)
Interval
Minimum
37.2
Maximum
42.8
Initial
1
40
5080
1
127
1
4347.2
0.93
5434.6
1.07
Interframe
127
127
118.1
135.9
15.3.5 Frame number time
The frame number time, tFN, is only used between frames and is based on a selectable
time from 0 to 63 ms and the number of the frame that was just transmitted as given in
Table 132. If the frame number time is not used, the value of the selected time should be
set to zero. The maximum number of frames is defined by the FNUM[3:0] control bits.
The range of the frame number time is a multiple of 0 to 63 ms using a clock generated
from the MFO divided by 125. The value of this time multiple can be changed by the
RFFT[5:0] bits in the RFCR6 register.
Table 132.ꢀFrame number interval times
Nominal frame number
Frame
Value of
FNUM[3:0]
Number
of frames
time interval added (ms)
interval where
time added
Minimum
n/a
Maximum
n/a
0
1
2
1
2
3
None
1 - 2
2 - 3
1
2
63
126
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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