NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
256
2
Maximum
258-bit format
RFB0 RFB1 RFB2 RFB3 RFB4 RFB5 RFBA RFBB RFBC RFBD RFBE RFBF
80
80-bit format
53-bit format
RFB0
RFB1 RFB2 RFB3 RFB4 RFB5 RFB6 RFB7 RFB8 RFB9
80
RFB0 RFB1 RFB2 RFB3 RFB4 RFB5
2
optional EOM
with all byte lengths
RFB6
bits [2:0]
2
Minimum
2-bit format
data in each byte defined by user software
RFB0
bits [1:0]
aaa-028031
Figure 38.ꢀData frame formats
15.2.1 Data buffer length
The number of bits sent in a given transmission frame is selected by the FRM[7:0]
control bits encoded as a direct binary number plus one. This gives a range of 2
through 256 bits. Data written to data buffer bits above the highest bit number will be
ignored. Transmission always begins with the data written in the RFB0 location. When
the requested number of bits have been transmitted an interrupt to the MCU can be
generated if the RFIE bit is set.
15.2.2 End of Message (EOM)
If the EOM control bit is set, then at the end of the data frame there will be carrier for
a period of two bit times at level high for the OOK modulation modes or fDATA1 for the
FSK modulation modes. Following the EOM period there will be no carrier for either the
OOK or FSK modes. If the EOM control bit is clear, no EOM period will be added to the
transmission.
15.3 Transmission randomization
When there are two or more different transmitters, the clock rates of each may drift into
synchronism with each other; and there is the possibility of RF data collisions and the
loss of data from both transmitters. In order to reduce possible RF data collisions each
transmission will contain from 1 to 16 frames of data. Each frame may be spaced at after
the initially timed transmission start time and between any two data frames as shown in
Figure 39.
FXTH87ERM
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© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
136 / 183
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