NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
programmed high temperature is reached the MCU will turn off all operating functions
and enter the STOP1 mode.
12.7.3 Temperature shutdown recovery
The MCU can be restarted by the Temperature Restart (TR) module when the
temperature returns within the normal temperature range, TRESET. When this occurs the
MCU will be reset and begin execution from the reset vector located at $DFFE/$DFFF.
The TR module can be enabled using the TRE bit in the SIMOPT1 register. The TR
module can be powered on and off by setting or clearing the TRE bit located at bit 3 in
the SIMOPT1 register at address $1802. The TRE bit is cleared by an MCU reset.
When the TRE bit is set the TR module can then be set to detect a recovery from either a
high temperature or a low temperature using the TRH in the SIMOPT1 register. The TRH
bit is cleared by an MCU reset.
The TR module does not activate an MCU restart and reset unless it has first moved
outside the re-arming temperature range, TREARM, as shown in Figure 23. The status of
the TR can be checked by reading the TRO bit located at bit 0 in the SIMTST register at
address $180F. The TRO bit is set high by an MCU reset. The state of the TRO bit is as
follows:
1 =TR module is outside the TREARM temperature range and will restart the MCU if the
TRE bit is set and temperature falls back within the TRESET temperature range.
0 =TR module is within the TRESET temperature range and the MCU cannot be armed to
restart when temperature falls back to the TRESET range. The TRE bit cannot be set.
TRH = 0
TREARML TRESETL
TRH = 1
TRO
TRESETH TREARMH
TREARM
TRESET
TRO = 1
active
shutdown
shutdown
TRO = 0
temperature
aaa-028016
Figure 23.ꢀTemperature restart response
As the temperature rises (lower arrow), TRO will transition from 0 to 1 when the
temperature crosses the TREARMH threshold. Then as the temperature falls (upper
arrow), TRO will transition transition from 1 to 0 when the temperature crosses the
TRESETH threshold.
This sequence is further explained by the user software flowchart in Figure 24.
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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