NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
5.5 STOP Modes
One of two stop modes are entered upon execution of a STOP instruction when the
STOPE bit in the system option register is set. In all STOP modes, all internal clocks
are halted except for the low frequency 1 kHz oscillator (LFO) which runs continuously
whenever power is applied to the VDD and VSS pins. If the STOPE bit is not set when
the CPU executes a STOP instruction, the MCU will not enter any of the STOP modes
and an illegal opcode reset is forced. The STOP modes are selected by setting the
appropriate bits in SPMSC2. Table 5 summarizes the behavior of the MCU in each of the
STOP1 and STOP4 modes.
5.5.1 STOP1 Mode
The STOP1 mode provides the lowest possible standby power consumption by causing
the internal circuitry of the MCU to be powered down.
When the MCU is in STOP1 mode, all internal circuits that are powered from the voltage
regulator are turned off. The voltage regulator is in a low-power standby state. STOP1 is
exited by asserting either a reset or an interrupt function to the MCU.
Entering STOP1 mode automatically asserts LVD. STOP1 cannot be exited until the VDD
is greater than VLVDH or VLV/DL rising (VDD must rise above the LVI re-arm voltage).
Upon wakeup from STOP1 mode, the MCU will start up as from a power-on reset (POR)
by taking the reset vector.
Note: If there are any pending interrupts that have yet to be serviced then the device will
not go into the STOP1 mode. Be certain that all interrupt flags have been cleared before
entry to STOP1 mode.
5.5.2 STOP4 LVD enabled in STOP mode
The LVD system is capable of generating either an interrupt or a reset when the supply
voltage drops below the LVD voltage. If the LVD is enabled by setting the LVDE and the
LVDSE bits in SPMSC1 when the CPU executes a STOP instruction, then the voltage
regulator remains active during STOP mode. If the user attempts to enter the STOP1
with the LVD enabled in STOP (LVDSE = 1), the MCU will enter STOP4 instead.
Table 5.ꢀSTOP mode behavior
Mode
STOP1
STOP4
LFO Oscillator, PWU
Always On and Clocking
Free-Running Counter (FRC)
Real-Time Interrupt (RTI)[1]
MFO Oscillator [2]
HFO Oscillator
Optionally On and Clocking
Always On if using LFO as Clock
Optionally On
Optionally On
Off
Off
Off
CPU
Standby
Standby
On
RAM
Off
Parameter Registers
FLASH
On
Off
Standby
Off
TPM1 2-Chan Timer/PWM
Digital I/O
Off
Disabled
Standby
FXTH87ERM
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© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
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