NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
• When the channel is configured for edge-aligned PWM, the channel flag is set when
the timer counter matches the channel value register that marks the end of the active
duty cycle period.
• When the channel is configured for center-aligned PWM, the timer count matches the
channel value register twice during each PWM cycle. In this CPWM case, the channel
flag is set at the start and at the end of the active duty cycle, which are the times when
the timer counter matches the channel value register.
The flag is cleared by the two-step sequence described in Section 11.6.1 "Clearing timer
interrupt flags".
12 Other MCU resources
It is not intended that physical parameter measurements be made during the time that
LFR may be actively receiving/decoding LF signals; or during the time that the RFM
may be actively powered up and/or transmitting RF data. The resulting interactions will
degrade the accuracy of the measurements.
The FXTH87E measures six physical parameters for use in the tire pressure monitoring
application: pressure, temperature, battery voltage, two external voltages and an optional
X- and/or Z-axis acceleration. Each parameter is accessed in a different manner and all
use firmware subroutine calls as described in Section 16 "Firmware". These subroutines
initialize some control bits within the sensor measurement interface, SMI, and then place
the MCU into the STOP4 mode until the measurement is completed with an interrupt
back to the MCU.
The accuracy, power consumption and timing specified for any measurement provided
in the data sheet are only guaranteed if the user obtains a reading using the specified
firmware subroutine call in Section 16 "Firmware". For additional information, contact
your NXP sales representative.
The FXTH87E uses a 6-channel, 10-bit analog-to-digital converter (ADC10) module.
The ADC10 module is an analog-to-digital converter using a successive approximation
register (SAR) architecture with sample and hold. Capture of pressure and acceleration
sensor readings is controlled by the sensor measurement interface (SMI) and capture of
temperature and voltage readings are controlled by the MCU.
When making measurements of the various analog voltages the individual blocks will
first be powered up long enough to stabilize their outputs before a conversion is started.
The ADC channels are connected in hardware. Conversions are started and ended
synchronously with the sampling of the voltages.
The accuracy, power consumption and timing specifications given in the data sheet are
based on using the assigned firmware subroutines in Section 16 "Firmware" to make
these measurements and convert them into an 8-bit, 9-bit or 10-bit transfer function.
These measurement accuracy specifications cannot be guaranteed if the user creates
custom software routines to convert these measurements. For additional information,
contact your NXP sales representative.
Table 96.ꢀADC10 channel assignments
ADC10
Channel
Input Select
Firmware Call(s)
Characteristic
Pressure Sensor
TPMS_READ_COMP_PRESSURE
PCODE
AD0
Optional X-axis Acceleration TPMS_READ_COMP_ACCEL_X
Sensor
AXCODE
FXTH87ERM
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© NXP B.V. 2019. All rights reserved.
Reference manual
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