NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
FXTH87ERM
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© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
106 / 183
Reset
No
No
No
No
Yes
Firmware
initialization
after a reset
Check
temperature?
Firmware
configuration of
device
Load TR trim
bits from
FLASH
Execute user's
TPMS program
Set TRE bit
TRE bit cleared
and TR trim bits
enabled to be
written
Temp
>T
REARMH
?
Temp
<T
REARML
?
Delay
TRO
bit set
Enter STOP1
mode
Clear TRE bit
Wake up from
STOP1 mode
TRO reset by
TR module
Read temperature
using
TPMS_COMP_TEMPERATURE
firmware
No
Yes
Yes
Yes
Yes
aaa-028017
Figure 24. Flowchart for using TR module
12.8 Free-Running Counter (FRC)
The Free-Running Counter (FRC) is a single channel up-counter, scaled to 2x of the
LFO (refer to the product data sheet for tolerances of f
LFO
), that supports enable, halt,
and clear functions. While the MCU is in the RUN mode, the FRC is controlled by first
writing a 1 to bit 0 of the PMCT register at address $180B, then by writing the defined
values to bits 7 and 5 of the same register. While the PMCT bit 0 is equal to 1, the 16-
bit counter value is available by reading addresses $1808 FRC_TIMER[7:0] and $1809
FRC_TIMER[15:8].
The two read-only FRC_TIMER registers contain the high and low bytes of the value in
the free-running counter. Reading either FRC_TIMER byte latches the contents of both
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