NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
It is recommended that this calculation be performed with a reasonable current load on
the battery of approximately 3 mA (RLOAD approximately 1000 ohms).
12.6 Measurement firmware
The firmware for making measurements is comprised of two function calls as described
in Section 16 "Firmware". Each measurement is a combination of a "read" that returns
the raw ADC output data and a "comp" routine which compensates that raw reading
based on information contained in the Universal Uncompensated Measurement Array
(UUMA) assigned in RAM memory.
The read routines fill specific locations in the UUMA with raw data; but the compensation
routines depend what is already present in the UUMA as shown in the data flow in
Figure 22.
The user, therefore, has the option to decide how often each measurement (and its
component terms) are made. The resulting power consumption is then the sum of using
these components are defined in the product data sheet.
A typical flow for a compensated pressure measurement would be:
1. Call the TPMS_READ_PRESSURE routine which yields a raw pressure value and fills
the UUMA with this data.
2. Call the TPMS_READ_TEMPERATURE routine which yields a raw temperature value
and fills the UUMA with this data.
3. Call the TPMS_READ_VOLTAGE routine which yields a raw voltage value and fills
the UUMA with this data.
4. Call the TPMS_COMP_PRESSURE routine which then takes the raw pressure,
temperature and voltage values from the UUMA and compensates to provide a true
pressure reading to the accuracy as specified in the product data sheet.
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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