NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
4.4.11 RESET pin
The RESET pin is used for test and establishing the BDM condition and providing the
programming voltage source to the internal FLASH memory. This pin can also be used to
direct to the MCU to the reset vector as described in Section 7.2 "MCU reset".
The RESET pin has an internal pullup device and can connected to VDD in the application
unless there is a need to enter BDM operation after the device as been soldered to the
PWB. If in-circuit BDM is desired the RESET pin can be left unconnected; but should be
connected to VDD through a low impedance resistor (< 10 kΩ) which can be over-driven
by an external signal. This low impedance resistor reduces the possibility of getting into
the debug mode in the application due to an EMC event.
Activation of the external reset function occurs when the voltage on the RESET pin goes
below 0.3 x VDD for at least 100 ns before rising above 0.7 x VDD as shown in Figure 7.
> 100 nsec
0.7 VDD
RESET
Reset
initiated
0.3 VDD
aaa-027996
Figure 7.ꢀRESET pin timing
4.4.12 PTB[1:0] pins
The PTB[1:0] pins are general purpose I/O pins. The PTB[1:0] pin functions become
high-impedance when the LF receiver has been enabled. These two pins can be
configured as nominal bidirectional I/O pins with programmable pullup. User software
must configure the general purpose I/O pins so that they do not result in "floating" inputs
as described in Section 8.1 "Unused pin configuration". Refer to Section 7 "Reset,
interrupts and system configuration" for details regarding pin multiplexing priorities.
5 Modes of operation
The operating modes of the FXTH87E are described in this section. Entry into each
mode, exit from each mode, and functionality while in each of the modes are described.
5.1 Features
• ACTIVE BACKGROUND DEBUG mode for code development
• STOP modes:
– System clocks stopped
– STOP1: Power down of most internal circuits, including RAM, for maximum power
savings; voltage regulator in standby
– STOP4: All internal circuits powered and full voltage regulation maintained for fastest
recovery
5.2 RUN mode
This is the normal operating mode for the FXTH87E. This mode is selected when the
BKGD/PTA4 pin is high at the rising edge of reset. In this mode, the CPU executes code
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
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