6. Power control (PWR)

6.1 Introduction

The Power control section (PWR) provides an overview of the supply architecture for the different power domains and of the supply configuration controller.

It also describes the features of the power supply supervisors and explains how the \( V_{\text{CORE}} \) supply domain is configured depending on the operating modes, the selected performance (clock frequency) and the voltage scaling.

6.2 PWR main features

• • Power supplies and supply domains
  • – Core domains ( \( V_{\text{CORE}} = V_{\text{CAP}} \) )
  • – \( V_{\text{DD}} \) domain
  • – Backup domain ( \( V_{\text{SW}}, V_{\text{BKP}} \) )
  • – Analog domain ( \( V_{\text{DDA}} \) )
• • System supply voltage regulation
  • – Switched-mode power supply power-efficient voltage down-converter (SMPS step-down converter)
  • – Voltage regulator (LDO)
• • Peripheral supply regulation
  • – USB regulator
• • Power supply supervision
  • – POR/PDR monitor
  • – BOR monitor
  • – PVD monitor
  • – AVD monitor
  • – \( V_{\text{BAT}} \) thresholds
  • – Temperature thresholds
• • Power management
  • – \( V_{\text{BAT}} \) battery charging
  • – Operating modes
  • – Voltage scaling control
  • – Low-power modes

6.3 PWR block diagram

Figure 17. Power control block diagram

6.3.1 PWR pins and internal signals

Table 28 lists the PWR inputs and output signals connected to package pins or balls, while Table 29 shows the internal PWR signals.

Table 28. PWR input/output signals connected to package pins or balls

1. 1. When LDO is available but VDDLDO pin is not present on the package, VDDLDO is internally connected to VDD.

Table 29. PWR internal input/output signals

Table 29. PWR internal input/output signals (continued)

6.4 Power supplies

The device requires \( V_{DD} \) and \( V_{DDSMPS} \) power supplies as well as independent supplies for \( V_{DDLDO} \) , \( V_{DDA} \) , \( V_{DDUSB} \) , and \( V_{CAP} \) . It also provides regulated supplies for specific functions (step-down converter, voltage regulator, USB regulator).

• • \( V_{DD} \) : external power supply for I/Os and system analog blocks such as reset, power management and oscillators
• • \( V_{BAT} \) : optional external power supply for backup domain when \( V_{DD} \) is not present ( \( V_{BAT} \) mode)

This power supply must be connected to \( V_{DD} \) when no battery is used.

• • \( V_{DDSMPS} \) : external power supply for the SMPS step-down converter
  \( V_{DDSMPS} \) must be connected to \( V_{DD} \) or tied to \( V_{SS} \) when the SMPS is not used.

• • \( V_{LXSMPS} \) : step-down converter supply output
• • \( V_{FBSMPS} \) : step-down converter sense feedback
• • \( V_{SSSMPS} \) : separate step-down converter ground
• • \( V_{DDLDO} \) : external power supply for voltage regulator
• • \( V_{CAP} \) : digital core domain supply

This power supply is independent from all the other power supplies:

• – When the voltage regulator is enabled, \( V_{CORE} \) is delivered by the internal voltage regulator.
• – When the voltage regulator is disabled, \( V_{CORE} \) is delivered by an external power supply through \( V_{CAP} \) pin, or by the SMPS step-down converter.

• • \( V_{DDA} \) : external analog power supply for ADCs, DACs, OPAMPS, comparators and voltage reference buffers

This power supply is independent from all the other power supplies.

• • \( V_{REF+} \) : external reference voltage for ADC and DAC.
  • – When the voltage reference buffer is enabled, \( V_{REF+} \) and \( V_{REF-} \) are delivered by the internal voltage reference buffer.
  • – When the voltage reference buffer is disabled, \( V_{REF+} \) is delivered by an independent external reference supply.

• • \( V_{SSA} \) : separate analog and reference voltage ground.
• • \( V_{DD50USB} \) : external power supply for USB regulator.
• • \( V_{DD33USB} \) : USB regulator supply output for USB interface.
  • – When the USB regulator is enabled, \( V_{DD33USB} \) is delivered by the internal USB regulator.
  • – When the USB regulator is disabled, \( V_{DD33USB} \) is delivered by an independent external supply input.
• • \( V_{SS} \) : common ground for all supplies except for step-down converter and analog peripherals.

Note: Depending on the operating power supply range, some peripherals might be used with limited features and performance. For more details, refer to section “General operating conditions” of the device datasheets.

Figure 18. Power supply overview

By configuring the SMPS step-down converter and LDO voltage regulator, the supply configurations shown in Figure 19 are supported for the V _CORE core domain and an external supply.

Note: The SMPS step-down converter is not available on all packages, and the Bypass mode is available only when the SMPS is available.

Figure 19. System supply configurations

MSV48170V1

The different supply configurations are controlled through the LDOEN, SDEN, SDEXTHP, SDLEVEL and BYPASS bits in PWR control register 3 (PWR_CR3) register according to Table 30 .

Table 30. Supply configuration control

Table 30. Supply configuration control (continued)

6.4.1 System supply startup

The system startup sequence from power-on in different supply configurations is the following (see Figure 20 and Figure 21 for LDO supply and Direct SMPS supply, respectively):

1. 1. When the system is powered on, the POR monitors V _DD supply. Once V _DD is above the POR threshold level, the SMPS step-down converter and voltage regulator are enabled in the default supply configuration:
   • – The SMPS step-down converter output level is set at 1.36 V.
   • – The voltage regulator output level is set at 1.0 V in accordance with the VOS3 level configured in PWR D3 domain control register (PWR_D3CR) .
2. 2. The system is kept in reset mode as long as V _CORE is not stable.
3. 3. Once V _CORE is stable, the system is taken out of reset and the HSI oscillator is enabled.
4. 4. Once the oscillator is stable, the system is initialized: Flash memory and option bytes are loaded and the CPU starts in limited Run mode (Run*).
5. 5. The software must then initialize the system including supply configuration programming in PWR control register 3 (PWR_CR3) . Once the supply configuration has been configured, the ACTVOSRDY bit in PWR control status register 1 (PWR_CSR1) must be checked to guarantee valid voltage levels:
   1. a) As long as ACTVOSRDY indicates that voltage levels are invalid, the system is in Run* mode, write operations to RAM are not allowed, and VOS must not be changed.
   2. b) Once ACTVOSRDY indicates that voltage levels are valid, the system is in normal Run mode, write accesses to RAMs are allowed and VOS can be changed.

V _CORE supplied from the voltage regulator (LDO)

When V _CORE is supplied from the voltage regulator (LDO), the V _CORE voltage settles directly at VOS3 level. However the SMPS step-down converter V _{FB SMPS} output voltage is set at 1.36 V. ACTVOSRDY bit in PWR control status register 1 (PWR_CSR1) indicates that the voltage levels are invalid.

The software has to program the supply configuration in PWR control register 3 (PWR_CR3) . In addition, the V _{FB SMPS} voltage level must reach the programmed SMPS step-down converter voltage output level (SDLEVEL) so that ACTVOSRDY indicates valid voltage levels (see Figure 20 ).

When exiting from Standby mode, the supply configuration is known by the system since the content of the PWR control register 3 (PWR_CR3) is retained. However the software must wait until ACTVOSRDY is set and ACTVOS reflects the awaited value in PWR control status register 1 (PWR_CSR1) to indicate V _CORE voltage levels are valid, before performing write accesses to RAM or changing VOS level.

Figure 20. Device startup with V _CORE supplied from voltage regulator

1. 1. In Run* mode, write operations to RAM are not allowed.
2. 2. Write operations to RAM are allowed and VOS can be changed only when ACTVOSRDY is valid.

V _CORE directly supplied from the SMPS step-down converter

When V _CORE is directly supplied from the SMPS step-down converter, the V _CORE voltage first settles at V _FBSMPS default level (1.36 V). Due to a too high supply compared to the VOS3 level, the ACTVOSRDY bit in PWR control status register 1 (PWR_CSR1) indicates invalid voltage levels. V _CORE settles at 1.0 V (VOS3 level) and ACTVODSRDY indicates valid voltage levels only when the supply configuration has been programmed in PWR control register 3 (PWR_CR3) (see Figure 21).

Figure 21. Device startup with V _CORE supplied directly from SMPS step-down converter

1. In Run* mode, write operations to RAM are not allowed.

2. Write operations to RAM are allowed and VOS can be changed only when ACTVOSRDY is valid.

When exiting from Standby mode, the supply configuration is known by the system since the content of PWR control register 3 (PWR_CR3) is retained. However the software must still wait for the ACTVOSRDY bit to be set in PWR control status register 1 (PWR_CSR1) to indicate \( V_{CORE} \) voltage levels are valid, before performing write accesses to RAM or changing VOS.

\( V_{CORE} \) supplied in Bypass mode (LDO and SMPS OFF)

The devices that feature the SMPS can also be used in Bypass mode.

When \( V_{CORE} \) is supplied in Bypass mode (LDO and SMPS OFF), the externally supplied \( V_{CORE} \) voltage must first settle at a default level higher than 1.1 V. Due to the LDO default state after power-up (enabled by default), the external \( V_{CORE} \) voltage must remain higher than 1.1 V until the LDO is disabled by software.

When the LDO is disabled, the external \( V_{CORE} \) voltage can be adjusted according to the user application needs (refer to section General operating conditions of the datasheet for details on \( V_{CORE} \) level versus the maximum operating frequency).

Figure 22. Device startup with \( V_{CORE} \) supplied in Bypass mode from external regulator

How to exit from Run* mode

As the Run* mode does not allow accessing RAM, PWR configuration must be done in the startup file. Below an example of code for SMPS supply that can be adapted for any other mode:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Exit Run* mode to Direct SMPS mode
;;
        THUMB
        PUBWEAK ExitRun0ModeToDirectSMPSMode
        SECTION .text:CODE:NOROOT:REORDER(1)
ExitRun0ModeToDirectSMPSMode
        MOV     R1, #0x4804
        MOVT    R1, #0x5802
        LDR     R0, [R1, #+8]
        BIC     R0, R0, #0x2
        STR     R0, [R1, #+8]
wait_actvosrdy:
        LDR     R2, [R1, #+0]
        LSLS    R0, R2, #+18
        BPL.N   wait_actvosrdy
        BX      LR

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Default interrupt handlers.
;;
        THUMB
        PUBWEAK Reset_Handler
        SECTION .text:CODE:NOROOT:REORDER(2)
Reset_Handler
        LDR     R0, =ExitRun0ModeToDirectSMPSMode
        BLX     R0
        LDR     R0, =SystemInit
        BLX     R0
        LDR     R0, =__iar_program_start
        BX      R0
  

6.4.2 Core domain

The \( V_{CORE} \) core domain supply can be provided by the SMPS step-down converter, LDO voltage regulator or by an external supply ( \( V_{CAP} \) ). \( V_{CORE} \) supplies all the digital circuitries

except for the backup domain and the Standby circuitry. The \( V_{CORE} \) domain is split into 3 sections:

• • D1 domain containing the CPU (Cortex®-M7), Flash memory and some peripherals.
• • D2 domain containing some peripherals
• • D3 domain containing the system control, I/O logic and low-power peripherals.

When a system reset occurs, the voltage regulator is enabled and supplies \( V_{CORE} \) . The SMPS step-down converter is also enabled to deliver 1.36 V. This allows the system to start up in any supply configurations (see Figure 19 ).

After a system reset, the software must configure the used supply configuration in PWR control register 3 (PWR_CR3) register before changing VOS in PWR D3 domain control register (PWR_D3CR) or the RCC ck_sys frequency. The different system supply configurations are controlled as shown in Table 30 .

Note: The SMPS step-down converter and the LDO are not available on all packages.

LDO voltage regulator

The embedded voltage regulator (LDO) requires external capacitors to be connected to VCAP pins.

The voltage regulator provides three different operating modes: Main (MR), Low-power (LP) or Off. These modes will be used depending on the system operating modes (Run, Stop and Standby).

• • Run and Autonomous modes

The LDO regulator is in Main mode and provides full power to the \( V_{CORE} \) domain (core, memories and digital peripherals). The regulator output voltage can be scaled by software to different voltage levels (VOS0, VOS1, VOS2, and VOS3) that are configured through VOS bits in PWR D3 domain control register (PWR_D3CR) . The VOS voltage scaling allows optimizing the power consumption when the system is clocked below the maximum frequency. By default VOS3 is selected after system reset. VOS can be changed on-the-fly to adapt to the required system performance.

• • Stop mode

The voltage regulator supplies the \( V_{CORE} \) domain to retain the content of registers and internal memories.

The regulator can be kept in Main mode to allow fast exit from Stop mode, or can be set in LP mode to obtain a lower \( V_{CORE} \) supply level and extend the exit-from-Stop latency. The regulator mode is selected through the SVOS and LPDS bits in PWR control register 1 (PWR_CR1) . Main mode and LP mode are allowed if SVOS3 voltage scaling is selected, while only LP mode is possible for SVOS4 and SVOS5 scaling. Due to a lower voltage level for SVOS4 and SVOS5 scaling, the Stop mode consumption can be further reduced.

• • Standby mode

The voltage regulator is OFF and the \( V_{CORE} \) domains are powered down. The content of the registers and memories is lost except for the Standby circuitry and the backup domain.

Note: The LDO is not available on all packages.

For more details, refer to the voltage regulator section in the datasheets.

SMPS step-down converter regulator

The SMPS step-down converter requires an external coil to be connected between the dedicated VLXSMPS pin and, via a capacitor, to VSS.

The SMPS step-down converter can be used in internal supply mode or external supply mode. The internal supply mode is used to directly supply the \( V_{CORE} \) domain, while the external supply mode is used to generate an intermediate supply level ( \( V_{DD\_extern} \) at 1.8 or 2.5 V) which can supply the voltage regulator and optionally an external circuitry.

The SMPS step-down converter works in three different power modes: Main (MR), Low-power (LP) or Off.

When the SMPS step-down converter is used in internal supply mode, the converter operating modes depend on the system modes (Run, Stop, Standby) and are configured through the associated VOS and SVOS levels:

• • Run mode
  The SMPS step-down converter operates in MR mode and provides full power to the \( V_{CORE} \) domain (core, memories and digital peripherals). The regulator output voltage can be scaled by software to different voltage levels (VOS0, VOS1, VOS2, and VOS3) that are configured through VOS bits in PWR D3 domain control register (PWR_D3CR) . The VOS voltage scaling allows optimizing the power consumption when the system is clocked below the maximum frequency. By default VOS3 is selected after system reset. VOS can be changed on-the-fly to adapt to the required system performance.
• • Stop mode
  The SMPS step-down converter supplies the \( V_{CORE} \) domain to retain the content of registers and internal memories. The regulator can be kept in MR mode to allow fast exit from Stop mode, or can be set in LP mode to achieve a lower \( V_{CORE} \) supply level and extend the exit-from-Stop latency. The regulator mode is selected through the SVOS and LPDS bits in PWR control register 1 (PWR_CR1) . MR mode or LP mode are allowed if SVOS3 voltage scaling is selected, while only LP mode is possible for SVOS4 and SVOS5 scaling. Due to a lower voltage level for SVOS4 and SVOS5 scaling, the Stop mode consumption can be further reduced.
• • Standby mode
  The SMPS step-down converter is OFF and the \( V_{CORE} \) domains are powered down. The content of the registers and memories are lost except for the Standby circuitry and the backup domain.

When the SMPS step-down converter supplies an external circuitry by generating an intermediate voltage level, the converter is forced ON and operates in MR mode. The intermediate voltage level is selected through SDLEVEL bits in PWR control register 3 (PWR_CR3) . \( V_{DD\_extern} \) is supplied at all times with full power whatever the system modes (Run, Stop, Standby).

Note: The SMPS step-down converter and the LDO are not available on all packages. When the LDO is not available, the SMPS supplies the voltage regulator and optionally an external circuitry.

6.4.3 PWR external supply

When \( V_{CORE} \) is supplied from an external source (Bypass mode), different operating modes can be used depending on the system operating modes (Run, Autonomous, Stop or Standby):

• • In Run and D3 Autonomous modes

The external source supplies full power to the \( V_{CORE} \) domain (core, memories and digital peripherals). The external source output voltage is scalable through different voltage levels ( \( V_{OS0} \) , \( V_{OS1} \) , \( V_{OS2} \) and \( V_{OS3} \) ). The externally applied voltage level must be reflected in the \( V_{OS} \) bits of \( PWR\_D3CR \) register. The RAMs must only be accessed for write operations when the external applied voltage level matches \( V_{OS} \) settings.

• • In Stop mode

The external source supplies \( V_{CORE} \) domain to retain the content of registers and internal memories. The regulator can select a lower \( V_{CORE} \) supply level to reduce the consumption in Stop mode.

• • In Standby mode

The external source must be switched OFF and the \( V_{CORE} \) domains powered down. The content of registers and memories is lost except for the Standby circuitry and the backup domain. The external source must be switched ON when exiting Standby mode.

6.4.4 Backup domain

To retain the content of the backup domain (RTC, backup registers and backup RAM) when \( V_{DD} \) is turned off, \( V_{BAT} \) pin can be connected to an optional voltage which is supplied from a battery or from an another source.

The switching to \( V_{BAT} \) is controlled by the power-down reset embedded in the Reset block that monitors the \( V_{DD} \) supply.

Warning: During \( t_{RSTTEMPO} \) (temporization at \( V_{DD} \) startup) or after a PDR is detected, the power switch between \( V_{BAT} \) and \( V_{DD} \) remains connected to \( V_{BAT} \) .

During the startup phase, if \( V_{DD} \) is established in less than \( t_{RSTTEMPO} \) (see the datasheet for the value of \( t_{RSTTEMPO} \) ) and \( V_{DD} > V_{BAT} + 0.6\text{ V} \) , a current may be injected into \( V_{BAT} \) through an internal diode connected between \( V_{DD} \) and the power switch ( \( V_{BAT} \) ).

If the power supply/battery connected to the \( V_{BAT} \) pin cannot support this current injection, it is strongly recommended to connect an external low-drop diode between this power supply and the \( V_{BAT} \) pin.

When the \( V_{DD} \) supply is present, the backup domain is supplied from \( V_{DD} \) . This allows saving \( V_{BAT} \) power supply battery life time.

If no external battery is used in the application, it is recommended to connect \( V_{BAT} \) externally to \( V_{DD} \) , and add a 100 nF external ceramic capacitor between \( V_{BAT} \) and \( V_{SS} \) .

When the \( V_{DD} \) supply is present and higher than the PDR threshold, the backup domain is supplied by \( V_{DD} \) and the following functions are available:

• • PC14 and PC15 can be used either as GPIO or as LSE pins.
• • PC13 can be used either as GPIO or as RTC_AF1 or RTC_TAMP1 pin assuming they have been configured by the RTC.
• • PC1/RTC_TAMP3 when it is configured by the RTC as tamper pins. PC1 can be used either as GPIO or as TAMP_IN3 assuming they have been configured by the RTC tamper.

Note: Since the switch only sinks a limited amount of current, the use of PC13 and PC15 GPIOs is restricted: only one I/O can be used as an output at a time, at a speed limited to 2 MHz with a maximum load of 30 pF. These I/Os must not be used as current sources (e.g. to drive an LED).

In \( V_{BAT} \) mode, when the \( V_{DD} \) supply is absent and a supply is present on \( V_{BAT} \) , the backup domain is supplied by \( V_{BAT} \) and the following functions are available:

• • PC14 and PC15 can be used as LSE pins only.
• • PC13 can be used as RTC_AF1 or RTC_TAMP1 pin assuming they have been configured by the RTC.
• • PC1/RTC_TAMP3 when it is configured by the RTC as tamper pins. PC1 can be used as TAMP_IN3 assuming it has been configured by the RTC tamper.

Accessing the backup domain

After reset, the backup domain (RTC registers and RTC backup registers) is protected against possible unwanted write accesses. To enable access to the backup domain, set the DBP bit in the PWR control register 1 (PWR_CR1) .

For more detail on RTC and backup RAM access, refer to Section 8: Reset and clock control (RCC) .

Backup RAM

The backup domain includes 4 Kbytes of backup RAM accessible in 32-bit, 16-bit or 8-bit data mode. The backup RAM is supplied from the backup regulator in the backup domain. When the backup regulator is enabled through BREN bit in PWR control register 2 (PWR_CR2) , the backup RAM content is retained even in Standby and/or \( V_{BAT} \) mode (it can be considered as an internal EEPROM if \( V_{BAT} \) is always present.)

The backup regulator can be ON or OFF depending whether the application needs the backup RAM function in Standby or \( V_{BAT} \) modes.

After a tamper event, the backup RAM can no more be used until an erase is explicitly requested: reading the backup RAM returns 0x0, and any write different from 0 is not effective. The backup RAM can be erased:

• • through the Flash memory interface when an RDP level regression from level 1 to level 0 is requested (refer to Section 4.5.3: Readout protection (RDP) ) or
• • by performing a simple dummy write with zero as data to any address of the backup RAM (this action resets the whole backup RAM when it is performed after a tamper event).

Figure 23. Backup domain

6.4.5 V _BAT battery charging

When V _DD is present, the external battery connected to V _BAT can be charged through an internal resistance.

V _BAT charging can be performed either through a 5 k \( \Omega \) resistor or through a 1.5 k \( \Omega \) resistor, depending on the VBRS bit value in PWR control register 3 (PWR_CR3) .

The battery charging is enabled by setting the VBE bit in PWR control register 3 (PWR_CR3) . It is automatically disabled in V _BAT mode.

6.4.6 Analog supply

Separate V _DDA analog supply

The analog supply domain is powered by dedicated V _DDA and V _SSA pads that allow the supply to be filtered and shielded from noise on the PCB, thus improving ADC and DAC conversion accuracy:

• • The analog supply voltage input is available on a separate V _DDA pin.
• • An isolated supply ground connection is provided on V _SSA pin.

Analog reference voltage V _REF+ /V _REF-

To achieve better accuracy low-voltage signals, the ADC and DAC also have a separate reference voltage, available on V _REF+ pin. The user can connect a separate external reference voltage on V _REF+ .

The V _REF+ controls the highest voltage, represented by the full scale value, the lower voltage reference ( V _REF- ) being connected to V _SSA .

When enabled by ENVR bit in the VREFBUF control and status register (see Section 32: Voltage reference buffer (VREFBUF) ), V _REF+ is provided from the internal voltage reference buffer. The internal voltage reference buffer can also deliver a reference voltage to external components through VREF+/VREF- pins.

When the internal voltage reference buffer is disabled by ENVR, V _REF+ is delivered by an independent external reference supply voltage.

Note: V _REF+ and V _REF- pins are not available on all packages (in this case they are connected internally respectively to VDDA and VSSA). Do not enable the internal voltage reference buffer when an external power supply is applied to the V _REF+ pin.

6.4.7 USB regulator

The USB transceivers are supplied from a dedicated V _DD33USB supply that can be provided either by the integrated USB regulator, or by an external USB supply.

When enabled by USBREGEN bit in PWR control register 3 (PWR_CR3) , the V _DD33USB is provided from the USB regulator, which is powered through the V _DD50USB pin generally connected to the USB VBUS line. Before using V _DD33USB , check that it is available by monitoring USB33RDY bit in PWR control register 3 (PWR_CR3) . The V _DD33USB supply level detector must be enabled through USB33DEN bit in PWR_CR3 register.

When the USB regulator is disabled through USBREGEN bit, V _DD33USB can be provided from an external supply. In this case V _DD33USB and V _DD50USB must be connected together. The V _DD33USB supply level detector must be enabled through USB33DEN bit in PWR_CR3 register before using the USB transceivers.

For more information on the USB regulator (see Section 62: USB on-the-go high-speed (OTG_HS) ).

Figure 24. USB supply configurations

MSV40339V1

6.5 Power supply supervision

Power supply level monitoring is available on the following supplies:

• • \( V_{DD} \) ( \( V_{DDSMPS} \) ) can be monitored via POR/PDR (see Section 6.5.1 ), BOR (see Section 6.5.2 ) and PVD monitor (see Section 6.5.3 )
• • \( V_{DDA} \) can be monitored via AVD monitor (see Section 6.5.4 )
• • \( V_{BAT} \) can be monitored via VBAT threshold (see Section 6.5.5 )
• • \( V_{SW} \) can be monitored via rst_vsw , which keeps \( V_{SW} \) domain in Reset mode as long as the level is not OK.
• • \( V_{BKP} \) can be monitored via a BRRDY bit in PWR control register 2 (PWR_CR2) .
• • \( V_{FBSMPS} \) can be monitored via a SDEXTRDY bit in PWR control register 3 (PWR_CR3) .
• • \( V_{DD33USB} \) can be monitored via USBRDY bit in PWR control register 3 (PWR_CR3) .

6.5.1 Power-on reset (POR)/power-down reset (PDR)

The system has an integrated POR/PDR circuitry that ensures proper startup operation.

The system remains in Reset mode when \( V_{DD} \) is below a specified \( V_{POR} \) threshold, without the need for an external reset circuit. Once the \( V_{DD} \) supply level is above the \( V_{POR} \) threshold, the system is taken out of reset (see Figure 25 ). For more details concerning the power-on/power-down reset threshold, refer to the electrical characteristics section of the datasheets.

The PDR can be enabled/disabled by the device PDR_ON input pin.

Figure 25. Power-on reset/power-down reset waveform

1. 1. For thresholds and hysteresis values, refer to the datasheets.

6.5.2 Brownout reset (BOR)

During power-on, the Brownout reset (BOR) keeps the system under reset until the \( V_{DD} \) supply voltage reaches the specified \( V_{BOR} \) threshold.

The \( V_{BOR} \) threshold is configured through system option bytes. By default, BOR is OFF. The following programmable \( V_{BOR} \) thresholds can be selected:

• • BOR OFF ( \( V_{BOR0} \) )
• • BOR Level 1 ( \( V_{BOR1} \) )
• • BOR Level 2 ( \( V_{BOR2} \) )
• • BOR Level 3 ( \( V_{BOR3} \) )

For more details on the brown-out reset thresholds, refer to the section “Electrical characteristics” of the product datasheets.

A system reset is generated when the BOR is enabled and \( V_{DD} \) supply voltage drops below the selected \( V_{BOR} \) threshold.

BOR can be disabled by programming the system option bytes. To disable the BOR function, \( V_{DD} \) must have been higher than \( V_{BOR0} \) to start the system option byte programming sequence. The power-down is then monitored by the PDR (see Section 6.5.1 ).

Figure 26. BOR thresholds

1. 1. For thresholds and hysteresis values, refer to the datasheets.

6.5.3 Programmable voltage detector (PVD)

The PVD can be used to monitor the \( V_{DD} \) power supply by comparing it to a threshold selected by the PLS[2:0] bits in the PWR control register 1 (PWR_CR1) . The PVD can also be used to monitor a voltage level on the PVD_IN pin. In this case PVD_IN voltage is compared to the internal \( V_{REFINT} \) level.

The PVD is enabled by setting the PVDE bit in PWR control register 1 (PWR_CR1) .

A PVDO flag is available in the PWR control status register 1 (PWR_CSR1) to indicate if \( V_{DD} \) or PVD_IN voltage is higher or lower than the PVD threshold. This event is internally connected to the EXTI and can generate an interrupt, assuming it has been enabled through the EXTI registers. The PVDO output interrupt can be generated when \( V_{DD} \) or PVD_IN voltage drops below the PVD threshold and/or when \( V_{DD} \) or PVD_IN voltage rises above the PVD threshold depending on EXTI rising/falling edge configuration. As an example the service routine could perform emergency shutdown tasks.

Figure 27. PVD thresholds

• 1. For thresholds and hysteresis values, refer to the datasheets.

6.5.4 Analog voltage detector (AVD)

The AVD can be used to monitor the \( V_{DDA} \) supply by comparing it to a threshold selected by the ALS[1:0] bits in the PWR control register 1 (PWR_CR1) .

The AVD is enabled by setting the AVDEN bit in PWR control register 1 (PWR_CR1) .

An AVDO flag is available in the PWR control status register 1 (PWR_CSR1) to indicate whether \( V_{DDA} \) is higher or lower than the AVD threshold. This event is internally connected to the EXTI and can generate an interrupt if enabled through the EXTI registers. The AVDO interrupt can be generated when \( V_{DDA} \) drops below the AVD threshold and/or when \( V_{DDA} \) rises above the AVD threshold depending on EXTI rising/falling edge configuration. As an example the service routine could indicate when the \( V_{DDA} \) supply drops below a minimum level.

Figure 28. AVD thresholds

1. 1. For thresholds and hysteresis values, refer to the datasheets.

6.5.5 Battery voltage thresholds

The battery voltage supply monitors the backup domain \( V_{SW} \) level. \( V_{SW} \) is monitored by comparing it with two threshold levels: \( V_{BATHigh} \) and \( V_{BATLow} \) . \( VBATH \) and \( VBATL \) flags in the PWR control register 2 (PWR_CR2) , indicate if \( V_{SW} \) is higher or lower than the threshold.

The \( V_{BAT} \) supply monitoring can be enabled/disabled via \( MONEN \) bit in PWR control register 2 (PWR_CR2) . When it is enabled, the battery voltage thresholds increase power consumption. As an example the \( V_{SW} \) levels monitoring could be used to trigger a tamper event for an over or under voltage of the RTC power supply domain (available in \( VBAT \) mode).

\( VBATH \) and \( VBATL \) are connected to RTC tamper signals (see Section 51: Real-time clock (RTC) ).

Note: Battery voltage monitoring is only available when the backup regulator is enabled ( \( BREN \) bit set in PWR control register 2 (PWR_CR2) ).

When the device does not operate in \( VBAT \) mode, the battery voltage monitoring checks \( V_{DD} \) level. When \( V_{DD} \) is available, \( V_{SW} \) is connected to \( V_{DD} \) through the internal power switch (see Section 6.4.4: Backup domain ).

Figure 29. \( VBAT \) thresholds

1. 1. For thresholds and hysteresis values, refer to the datasheets.

6.5.6 Temperature thresholds

The junction temperature can be monitored by comparing it with two threshold levels, \( TEMP_{high} \) and \( TEMP_{low} \) . \( TEMPH \) and \( TEMPL \) flags, in the PWR control register 2 (PWR_CR2) , indicate whether the device temperature is higher or lower than the threshold. The temperature monitoring can be enabled/disabled via \( MONEN \) bit in PWR control register 2 (PWR_CR2) . When enabled, the temperature thresholds increase power consumption. As an example the levels could be used to trigger a routine to perform temperature control tasks.

The temperature thresholds are available only when the backup regulator is enabled ( \( BREN \) bit set in the PWR_CR2 register).

\( TEMPH \) and \( TEMPL \) wakeup interrupts are available on the RTC tamper signals (see Section 51: Real-time clock (RTC) ).

Figure 30. Temperature thresholds

1. For thresholds and hysteresis values, refer to the datasheets.

6.5.7 \( V_{CORE} \) maximum voltage level detector

\( V_{CORE} \) is protected against too high voltages in the direct SMPS step-down converter supply configuration. \( V_{CORE} \) overvoltage protection is enabled at startup by hardware once the SMPS step-down converter configuration has been programmed into PWR control register 3 (PWR_CR3) :

• • \( V_{CORE} \) voltage level stays within range:
  • – \( ACTVOSRDY \) bit in PWR control status register 1 (PWR_CSR1) indicate valid voltage levels.
  • – The system operates normally and \( V_{CORE} \) overvoltage protection is disabled.
• • \( V_{CORE} \) overvoltage (due to a wrongly programmed SMPS step-down converter configuration):

• – The hardware forces the SMPS step-down converter voltage level to 1.0 V.
• – The ACTVOSRDY goes on indicating invalid voltage levels. In this case the software must be corrected and re-loaded to program a correct SMPS step-down converter configuration that matches the application supply connections. The system must then be power cycled.

6.6 Power management

The power management block controls the \( V_{CORE} \) supply in accordance with the system operation modes (see Section 6.6.1 ).

The \( V_{CORE} \) domain is split into the following power domains.

• • D1 domain containing some peripherals and the Cortex®-M7 Core.
• • D2 domain containing a large part of the peripherals.
• • D3 domain containing some peripherals and the system control.

The D1, D2 and system D3 power domains can operate in one of the following operating modes:

• • DRun/Run/Run* (power ON, clock ON)
• • DStop/Stop (power ON, clock OFF)
• • DStandby/Standby (Power OFF, clock OFF).

The operating modes for D1 domain and D2 domain are independent. However system D3 domain power modes depend on D1 and D2 domain modes:

• • For system D3 domain to operate in Stop mode, both D1 and D2 domains must be in DStop or DStandby mode.
• • For system D3 domain to operate in Standby mode, both D1 and D2 domains must be in DStandby too.

D1, D2 and system D3 domains are supplied from a single regulator at a common \( V_{CORE} \) level. The \( V_{CORE} \) supply level follows the system operating mode (Run, Stop, Standby). The D1 domain and/or D2 domain supply can be powered down individually when the domains are in DStandby mode.

The following voltage scaling features allow controlling the power with respect to the required system performance (see Section 6.6.2: Voltage scaling ):

• • To obtain a given system performance, the corresponding voltage scaling must be set in accordance with the system clock frequency. To do this, configure the VOS bits to the Run mode voltage scaling.
• • To obtain the best trade-off between power consumption and exit-from-Stop mode latency, configure the SVOS bits to Stop mode voltage scaling.

6.6.1 Operating modes

Several system operating modes are available to tune the system according to the performance required, i.e. when the CPU does not need to execute code and are waiting for an external event. It is up to the user to select the operating mode that gives the best compromise between low power consumption, short startup time and available wakeup sources.

The operating modes allow controlling the clock distribution to the different system blocks and powering them. The system operating mode is driven by the CPU subsystem, D2 subsystem and system D3 autonomous wakeup. A CPU subsystem can include multiple domains depending on its peripheral allocation (see Section 8.5.11: Peripheral clock gating control ).

The following operating modes are available for the different system blocks (see Table 31 ):

• • CPU subsystem modes:
  • – CRun
    CPU and CPU subsystem peripheral allocated via RCC PERxEN bits are clocked.
  • – CSleep
    The CPU clock is stalled and the CPU subsystem allocated peripheral(s) clock operate according to RCC PERxLPEN.
  • – CStop
    CPU and CPU subsystem peripheral clocks are stalled.
• • D1 domain mode:
  • – DRun
    The domain bus matrix is clocked. The CPU subsystem operates in CRun or CSleep mode.
  • – DStop
    The domain bus matrix clock is stalled.
    The CPU subsystem operates in CStop mode and the PDDS_D1 ^(a) bit selects DStop mode.
  • – DStandby
    The domain is powered down.
    The CPU subsystem operates in CStop mode and the PDDS_D1 bit selects DStandby mode.
• • D2 domain mode:
  • – DRun
    The domain bus matrix is clocked.
    The CPU subsystem has an allocated peripheral in the D2 domain and the CPU subsystem operates in CRun or CSleep mode.

a. The PDDS_Dn bits belong to PWR CPU control register (PWR_CPUCR) .

• – DStop
  The domain bus matrix clock is stalled.
  The CPU subsystem has no peripherals allocated in the D2 domain and PDDS_D2 ^(a) bit selects DStop mode,
  or
  the CPU subsystem has an allocated peripheral in D2 domain, the CPU subsystem operates in CStop mode and PDDS_D2 bit selects DStop mode.
• – DStandby
  The domain is powered down.
  The CPU subsystem has no peripherals allocated in the D2 domain and PDDS_D2 bit selects DStandby mode,
  or
  the CPU subsystem has an allocated peripheral in the D2 domain, the CPU subsystem operates in CStop mode and PDDS_D2 bit selects DStandby mode.
• • System /D3 domain modes
  • – Run/Run*
    The system clock and D3 domain bus matrix clock are running:
    • - The CPU subsystem is in CRun or CSleep mode
    • or
    • - A wakeup signal is active. (i.e. System D3 Autonomous mode)
    The Run* mode is entered after a POR reset and a wakeup from Standby. In Run* mode, the performance is limited and the system supply configuration shall be programmed in PWR control register 3 (PWR_CR3) . The system enters Run mode only when the ACTVOSRDY bit in PWR control status register 1 (PWR_CSR1) is set to 1.
  • – Stop
    The system clock and D3 domain bus matrix clock is stalled:
    • - The CPU subsystem is in CStop mode.
    • and
    • - all wakeup signals are inactive.
    • and
    • - At least one PDDS_Dn ^(a) bit for any domain select Stop mode.
  • – Standby
    The system is powered down:
    • - The CPU subsystem is in CStop mode
    • and
    • - all wakeup signals are inactive.
    • and
    • - All PDDS_Dn ^(a) bits for all domains select Standby mode.

In Run mode, power consumption can be reduced by one of the following means:

• • Lowering the system performance by slowing down the system clocks and reducing the V _CORE supply level through VOS voltage scaling bits.
• • Gating the clocks to the APBx and AHBx peripherals when they are not used, through PERxEN bits.

Table 31. Summary of the operating mode

1. In the D2 domain, the CPU subsystem has an allocated peripheral in the domain and operates in CRun or CSleep mode.

2. The CPU subsystem peripherals that have a PERxLPEN bit will operate accordingly.

3. The CPU subsystem peripherals located in the D3 domain that have a PERxAMEN bit operate accordingly.

4. All domains need to be in DStop Or DStandby.

5. When the CPU is in CStop and D3 domain in Autonomous mode, the last EXTI Wakeup source is cleared.

6. When the system oscillator HSI or CSI is used, the state is controlled by HSIKERON and CSICKERON, otherwise the system oscillator is OFF.

7. All domains are in DStandby mode.

6.6.2 Voltage scaling

The D1, D2, and D3 domains are supplied from a single voltage regulator supporting voltage scaling with the following features:

• • Run mode voltage scaling
  • – VOS0: Scale 0 ( \( V_{\text{CORE}} \) boost)
  • – VOS1: Scale 1
  • – VOS2: Scale 2
  • – VOS3: Scale 3
• • Stop mode voltage scaling
  • – SVOS3: Scale 3
  • – LP-SVOS4: Scale 4
  • – LP-SVOS5: Scale 5

For more details on voltage scaling values, refer to the product datasheets.

After reset, the system starts on the lowest Run mode voltage scaling (VOS3). The voltage scaling can then be changed on-the-fly by software by programming VOS bits in PWR D3 domain control register (PWR_D3CR) according to the required system performance. When exiting from Stop mode or Standby mode, the Run mode voltage scaling is reset to the default VOS3 value.

Before entering Stop mode, the software can preselect the SVOS level in PWR control register 1 (PWR_CR1) . The Stop mode voltage scaling for SVOS4 and SVOS5 also sets the voltage regulator in Low-power (LP) mode to further reduce power consumption. When preselecting SVOS3, the use of the voltage regulator low-power mode (LP) can be selected by LPDS register bit.

6.6.3 Power control modes

The power control block handles the \( V_{CORE} \) supply for system Run, Stop and Standby modes.

The system operating mode depends on the CPU subsystem modes (CRun, CSleep, CStop), on the domain modes (DRun, DStop, DStandby), and on the system D3 autonomous wakeup:

• • In Run mode and Autonomous mode, \( V_{CORE} \) is defined by the VOS voltage scaling. The CPU subsystem is in CRun or CSleep or an EXTI wakeup is active.
• • In Stop mode, \( V_{CORE} \) is defined by the SVOS voltage scaling. The CPU subsystem is in CStop mode and no EXTI wakeup is pending. The D1 domain and D2 domain are either in DStop or DStandby mode.
• • In Standby mode, \( V_{CORE} \) supply is switched off. The CPU subsystem is in CStop mode and no EXTI wakeup is pending. The D1 domain and D2 domain are both in DStandby mode.

The domain operating mode can depend on the CPU subsystem when peripherals are allocated in the corresponding domain. The domain mode selection between DStop and DStandby is configured via domain dedicated PDDS_Dn bits in PWR CPU control register (PWR_CPUCR) . The CPU can choose to keep a domain in DStop, or allow a domain to enter DStandby mode.

If a domain is in DStandby mode, the corresponding power is switched off.

All the domains can be configured for the system mode (Stop or Standby) through PDDS_Dn bits in PWR CPU control register (PWR_CPUCR) . The system enters Standby only when all PDDS_Dn bits for all domains have allowed it.

Table 32. PDDS_Dn low-power mode control

Figure 33. Power control modes detailed state diagram

After a system reset, the CPU is in CRun mode.

Power control state transitions are initiated by the following events:

• • CPU going to CStop mode (state transitions in Run mode are marked in green and red)
  • – Green transitions: CPU wakes up as from CSleep.
  • – Red transitions: CPU wakes up with domain reset. The SBF_Dn is set.
• • Allocating or deallocating a peripheral in a domain (state transitions in Run mode are marked in orange and red)
  • – Orange transitions: the domain wakes up from DStop
  • – Red transitions: the domain wakes up from DStandby. The SBF_Dn is set.
• • The system enters or exits from Stop mode (state transitions marked in blue)
  • – Blue transitions the system wakes up from Stop mode. The STOPF is set.
• • The system enters or exits from Standby mode (state transitions in Stop and Standby mode are marked in red).
  • – When exiting from Standby mode, the SBF is set.

When a domain exits from DStandby, the domain peripherals are reset, while the domain SBF_Dn bit is set (state transitions causing a domain reset are marked in red).

Table 33 shows the flags that indicate from which mode the domain/system exits. The CPU features a set of flags which can be read from PWR CPU control register (PWR_CPUCR) .

Table 33. Low-power exit mode flags

1. When returning from Standby, the SBF_D1 and SBF_D2 reflect the reset value.

6.6.4 Power management examples

• • Figure 34 shows \( V_{CORE} \) voltage scaling behavior in Run mode.
• • Figure 35 shows \( V_{CORE} \) voltage scaling behavior in Stop mode.
• • Figure 36 shows \( V_{CORE} \) voltage regulator and voltage scaling behavior in Standby mode.
• • Figure 37 shows \( V_{CORE} \) voltage scaling behavior in Run mode with D1 and D2 domains are in DStandby mode

Example of \( V_{CORE} \) voltage scaling behavior in Run mode

Figure 34 illustrates the following system operation sequence example:

1. 1. After reset, the system starts from HSI with VOS3.
2. 2. The system performance is first increased to a medium-speed clock from the PLL with voltage scaling VOS2. To do this:
   1. a) Program the voltage scaling to VOS2.
   2. b) Once the \( V_{CORE} \) supply has reached the required level indicated by VOSRDY, increase the clock frequency by enabling the PLL.
   3. c) Once the PLL is locked, switch the system clock.
3. 3. The system performance is then increased to high-speed clock from the PLL with voltage scaling VOS1. To do this:
   1. a) Program the voltage scaling to VOS1.
   2. b) Once the \( V_{CORE} \) supply has reached the required level indicated by VOSRDY, increase the clock frequency.
4. 4. The system performance is then reduced to a medium-speed clock with voltage scaling VOS2. To do this:
   1. a) First decrease the system frequency.
   2. b) Then decrease the voltage scaling to VOS2.
5. 5. The next step is to reduce the system performance to HSI clock with voltage scaling VOS3. To do this:
   1. a) Switch the clock to HSI.
   2. b) Disable the PLL.
   3. c) Decrease the voltage scaling to VOS3.
6. 6. The system performance can then be increased to high-speed clock from the PLL. To do this:
   1. a) Program the voltage scaling to VOS1.
   2. b) Once the \( V_{CORE} \) supply has reached the required level indicated by VOSRDY, increase the clock frequency by enabling the PLL.
   3. c) Once the PLL is locked, switch the system clock.

When the system performance (clock frequency) is changed, VOS shall be set accordingly, otherwise the system might be unreliable.

Figure 34. Dynamic voltage scaling in Run mode

1. The status of the register bits at each step is shown in blue.

Example of V _CORE voltage scaling behavior in Stop mode

Figure 35 illustrates the following system operation sequence example:

1. 1. The system is running from the PLL in high-performance mode (VOS1 voltage scaling).
2. 2. The CPU subsystem deallocates all the peripheral in the D2 domain that will first enter DStop mode. D2 system clock is stopped. The system still provides the high-performance system clock, hence the voltage scaling shall stay at VOS1 level.
3. 3. In a second step, the CPU subsystem enters CStop mode, D1 domain enters DStop mode and the system enters Stop mode. The system clock is stopped and the hardware lowers the voltage scaling to the software preselected SVOS4 level.
4. 4. The CPU subsystem is then woken up. The system exits from Stop mode, the D1 domain exits from DStop mode and the CPU subsystem exits from CStop mode. The hardware then sets the voltage scaling to VOS3 level and waits for the requested supply level to be reached before enabling the HSI clock. Once the HSI clock is stable, the system clock and the D1 system clock are enabled.
5. 5. The CPU subsystem allocates a peripheral in the D2 domain. The D2 system clock is enabled.
6. 6. The system performance is then increased. To do this:
   1. a) The software first sets the voltage scaling to VOS1.
   2. b) Once the V _CORE supply has reached the required level indicated by VOSRDY, the clock frequency can be increased by enabling the PLL.
   3. c) Once the PLL is locked, the system clock can be switched.

Figure 35. Dynamic voltage scaling behavior with D1, D2 and system in Stop mode

1. 1. The status of the register bits at each step is shown in blue.

Example of V _CORE voltage regulator and voltage scaling behavior in Standby mode

Figure 36 illustrates the following system operation sequence example:

1. 1. The system is running from the PLL in high-performance mode (VOS1 voltage scaling).
2. 2. The CPU subsystem deallocates all the peripherals in the D2 domain that will first enter DStandby mode. The D2 domain bus matrix clock is stopped and the power is switched off. The system performance is unchanged hence the voltage scaling does not change.
3. 3. The CPU subsystem then enters CStop mode, D1 domain enters DStandby mode and the system enters Standby mode. The system clock is stopped and the voltage regulator switched off.
4. 4. The system is then woken up by a wakeup source. The system exits from Standby mode. The hardware sets the voltage scaling to the default VOS3 level and waits for the requested supply level to be reached before enabling the default HSI oscillator. Once the HSI clock is stable, the system clock and D1 subsystem clock are enabled.

Since there are no allocated peripherals in the D2 domain, this domain remains in DStop mode. The software shall then check the ACTVOSRDY is valid before changing the system performance.

1. 5. In a next step, increase the system performance. To do this:
   1. a) The software first increases the voltage scaling to VOS1 level
   2. b) Before enabling the PLL, it waits for the requested supply level to be reached by monitoring VOSRDY bit.
   3. c) Once the PLL is locked, the system clock can be switched.
2. 6. The CPU subsystem puts the D2 domain in DStandby mode.

Figure 36. Dynamic Voltage Scaling D1, D2, system Standby mode

MSV40898V3

1. 1. The status of the register bits at each step is shown in blue.

Example of \( V_{CORE} \) voltage scaling behavior in Run mode with D1 and D2 domains in DStandby mode

Figure 37 illustrates the following system operation sequence example:

1. 1. The system is running from the PLL with system in high performance mode (VOS1 voltage scaling).
2. 2. The CPU subsystem deallocates all the peripherals in the D2 domain that will first enter DStandby mode. The D2 domain bus matrix clock is stopped and its power switched off. The system performance is unchanged hence the voltage scaling does not change.
3. 3. The CPU subsystem then enters CStop mode and the D1 domain enters DStandby mode. The D1 domain bus matrix clock is stopped and its power switched off. At the same time the system enters Stop mode. The system clock is stopped and the hardware lowers the voltage scaling to the software preselected SVOS4 level.
4. 4. The system is then woken up by a D3 Autonomous mode wakeup event. The system exits from Stop mode. The hardware sets the voltage scaling to the default VOS3 level and waits for the requested supply level to be reached before enabling the HSI clock. Once the HSI clock is stable, the system clock is enabled. The system is running in D3 Autonomous mode.
5. 5. The D3 Autonomous mode wakeup source is then cleared, causing the system to enter Stop mode. The system clock is stopped and the voltage scaling is lowered to the software preselected SVOS4 level.
6. 6. The CPU subsystem is then woken up. The system exits from Stop mode, the D1 domain exits from DStandby mode and the CPU subsystem exits from CStop mode. The hardware sets the voltage scaling to the default VOS3 level and waits for the requested supply level to be reached before enabling the default HSI oscillator. Once the HSI clock is stable, the system clock and the D1 subsystem clock are enabled. The D2 domain remains in DStandby mode.

Figure 37. Dynamic voltage scaling behavior with D1 and D2 in DStandby mode and D3 in Autonomous mode

MSV40899V3

1. 1. The status of the register bits at each step is shown in blue.

6.7 Low-power modes

Several low-power modes are available to save power when the CPU does not need to execute code (i.e. when waiting for an external event). It is up to the user application to select the mode that gives the best compromise between low power consumption, short startup time and available wakeup sources:

• • Slowing down system clocks (see Section 8.5.6: System clock (sys_ck) )
• • Controlling individual peripheral clocks (see Section 8.5.11: Peripheral clock gating control )
• • Low-power modes
  • – CSleep (CPU clock stopped)
  • – CStop (CPU subsystem clock stopped)
  • – DStop (Domain bus matrix clock stopped)
  • – Stop (System clock stopped)
  • – DStandby (Domain powered down)
  • – Standby (System powered down)

6.7.1 Slowing down system clocks

In Run mode, the speed of the system clock ck_sys can be reduced. For more details refer to Section 8.5.6: System clock (sys_ck) .

6.7.2 Controlling peripheral clocks

In Run mode, the HCLKx and PCLKx for individual peripherals can be stopped by configuring at any time PERxEN bit in RCC_C1_xxxxENR or RCC_xxxxENR to reduce power consumption.

To reduce power consumption in CSleep mode, the individual peripheral clocks can be disabled by configuring PERxLPEN bit in RCC_C1_xxxxLPENR or RCC_xxxxLPENR . For the peripherals still receiving a clock in CSleep mode, their clock can be slowed down before entering CSleep mode.

6.7.3 Entering low-power modes

CPU subsystem CSleep and CStop low-power modes are entered by the MCU when executing the WFI (Wait For Interrupt) or WFE (Wait for Event) instructions, or when the SLEEPONEXIT bit in the Cortex ^® -M System Control register is set on Return from ISR.

The D2 domain enters DStop or DStandby when the CPU subsystem has no peripheral allocated in the domain or is in CStop. The D1 domain enters DStop or DStandby when the CPU subsystem is in CStop.

The system can enter Stop or Standby low-power mode when all EXTI wakeup sources are cleared and the other domains are in DStop or DStandby mode.

6.7.4 Exiting from low-power modes

The CPU subsystem exits from CSleep mode through any interrupt or event depending on how the low-power mode was entered:

• • If the WFI instruction or Return from ISR was used to enter to low-power mode, any peripheral interrupt acknowledged by the NVIC can wake up the system.
• • If the WFE instruction is used to enter to low-power mode, the CPU exits from low-power mode as soon as an event occurs. The wakeup event can be generated either by:
  • – An NVIC IRQ interrupt.

When SEVONPEND = 0 in the Cortex®-M7 System Control register, the interrupt must be enabled in the peripheral control register and in the NVIC.

When the MCU resumes from WFE, the peripheral interrupt pending bit and the NVIC peripheral IRQ channel pending bit in the NVIC interrupt clear pending register have to be cleared. Only NVIC interrupts with sufficient priority will wakeup and interrupt the MCU.

When SEVONPEND = 1 in the Cortex®-M7 System Control register, the interrupt must be enabled in the peripheral control register and optionally in the NVIC.

When the MCU resumes from WFE, the peripheral interrupt pending bit and, when enabled, the NVIC peripheral IRQ channel pending bit (in the NVIC interrupt clear pending register) have to be cleared.

All NVIC interrupts will wakeup the MCU, even the disabled ones.

Only enabled NVIC interrupts with sufficient priority will wakeup and interrupt the MCU.

• – An event

An EXTI line must be configured in event mode. When the CPU resumes from WFE, it is not necessary to clear the EXTI peripheral interrupt pending bit or the NVIC IRQ channel pending bit as the pending bits corresponding to the event line is not set. It might be necessary to clear the interrupt flag in the peripheral.

The CPU subsystem exits from CStop, DStop and Stop modes by enabling an EXTI interrupt or event depending on how the low-power mode was entered (see above).

The system can wake up from Stop mode by enabling an EXTI wakeup, without waking up a CPU subsystem. In this case the system will operate in D3 Autonomous mode.

The CPU subsystem exits from DStandby mode by enabling an EXTI interrupt or event, regardless on how DStandby mode was entered. Program execution restarts from CPU local reset (such as a reset vector fetched from System configuration block (SYSCFG)).

The D2 domain can exit from DStop or DStandby mode when the CPU allocates a first peripheral in the domain.

The CPU subsystem exits from Standby mode by enabling an external reset (NRST pin), an IWDG reset, a rising edge on one of the enabled WKUPx pins or a RTC event. Program execution restarts in the same way as after a system reset (such as boot pin sampling, option bytes loading or reset vector fetched).

6.7.5 CSleep mode

The CSleep mode applies only to the CPU subsystem. In CSleep mode, the CPU clock is stopped. The CPU subsystem peripheral clocks operate according to the values of PERxLPEN bits in RCC_C1_xxxxENR or RCC_xxxxENR.

Entering CSleep mode

The CSleep mode is entered according to Section 6.7.3: Entering low-power modes , when the SLEEPDEEP bit in the Cortex ^® -M System Control register is cleared.

Refer to Table 34 for details on how to enter to CSleep mode.

Exiting from CSleep mode

The CSleep mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 34 for more details on how to exit from CSleep mode.

Table 34. CSleep mode

6.7.6 CStop mode

The CStop mode applies only to the CPU subsystem. In CStop mode, the CPU clock is stopped. Most CPU subsystem peripheral clocks are stopped too and only the CPU subsystem peripherals having a PERxAMEN bit operate accordingly.

In CStop mode, CPU subsystem peripherals having a kernel clock request can still request their kernel clock. For the peripheral having a PERxAMEN bit, this bit must be set to be able to request the kernel clock.

Entering CStop mode

The CStop mode is entered according to Section 6.7.3: Entering low-power modes , when the SLEEPDEEP bit in the Cortex ^® -M System Control register is set.

Refer to Table 35 for details on how to enter to CStop mode.

Exiting from CStop mode

The CStop mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 35 for more details on how to exit from CStop mode.

Table 35. CStop mode

6.7.7 DStop mode

D1 domain and/or D2 domain enters DStop mode only when the CPU subsystem is in CStop mode and has allocated peripheral in the domain (see Table 36 ). In DStop mode the domain bus matrix clock is stopped.

The Flash memory can enter low-power Stop mode when it is enabled through FLPS in PWR_CR1 register. This allows a trade-off between domain DStop restart time and low power consumption.

In DStop mode domain peripherals using the LSI or LSE clock and peripherals having a kernel clock request are still able to operate.

Entering DStop mode

The DStop mode is entered according to Section 6.7.3: Entering low-power modes , when at least one PDDS_Dn bit in PWR CPU control register (PWR_CPUCR) for the domain select Stop.

Refer to Table 37 for details on how to enter DStop mode.

If Flash memory programming is ongoing, the DStop mode entry is delayed until the memory access is finished.

If an access to the domain bus matrix is ongoing, the DStop mode entry is delayed until the domain bus matrix access is complete.

Exiting from DStop mode

The DStop mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 37 for more details on how to exit from DStop mode.

When exiting from DStop mode, the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling depend on the system mode.

• • When the system did not enter Stop mode, the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling values are the same as when entering DStop mode.
• • When the system has entered Stop mode, the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling are reset.

Table 37. DStop mode

6.7.8 Stop mode

The system D3 domain enters Stop mode only when the CPU subsystem is in CStop mode, the EXTI wakeup sources are inactive and at least one PDDS_Dn bit in PWR CPU control register (PWR_CPUCR) for any domain request Stop. In Stop mode, the system clock including a PLL and the D3 domain bus matrix clocks are stopped.

The HSI or CSI can remain enabled in system Stop mode (HSIKERON and CSIKERON set in RCC_CR register). After exiting Stop mode, the clock is quickly available as kernel clock for peripherals. Other system oscillator sources are stopped and require a starting time after exiting Stop mode.

In system D3 domain Stop mode, D1 domain and D2 domain are either in DStop and/or DStandby mode.

In Stop mode, the domain peripherals that use the LSI or LSE clock, and the peripherals that have a kernel clock request to select HSI or CSI as source, are still able to operate.

In system Stop mode, the following features can be selected to remain active by programming individual control bits:

• • Independent watchdog (IWDG)
  The IWDG is started by writing to its Key register or by hardware option. Once started it cannot be stopped except by a Reset (see Section 50.3 in Section 50: Independent watchdog (IWDG) ).
• • Real-time clock (RTC)
  This is configured via the RTCEN bit in the RCC backup domain control register (RCC_BDCR) .
• • Internal RC oscillator (LSI RC)
  This is configured via the LSION bit in the RCC Clock Control and Status Register (RCC_CSR) .
• • External 32.768 kHz oscillator (LSE OSC)
  This is configured via the LSEON bit in the RCC backup domain control register (RCC_BDCR) .

• • Peripherals capable of running on the LSI or LSE clock.
• • Peripherals having a kernel clock request.
• • Internal RC oscillators (HSI and CSI)

This is configured via the HSIKERON and CSIKERON bits in the RCC Clock Control and Status Register (RCC_CSR) .

• • The ADC or DAC can also consume power during Stop mode, unless they are disabled before entering this mode. To disable them, the ADON bit in the ADC_CR2 register and the ENx bit in the DAC_CR register must both be written to 0.

The selected SVOS4 and SVOS5 levels add an additional startup delay when exiting from system Stop mode (see Table 38 ).

Table 38. Stop mode operation

Entering Stop mode

The Stop mode is entered according to Section 6.7.3: Entering low-power modes , when at least one PDDS_Dn bit n PWR CPU control register (PWR_CPUCR) for any domain request Stop.

Refer to Table 39 for details on how to enter Stop mode.

If Flash memory programming is ongoing, the Stop mode entry is delayed until the memory access is finished.

If an access to a bus matrix (AXI, AHB or APB) is ongoing, the Stop mode entry is delayed until the bus matrix access is finished.

To allow peripherals having a kernel clock request to operate in Stop mode, the system must use SVOS3 level.

Note: Use a DSB instruction to ensure that outstanding memory transactions complete before entering stop mode.

Exiting from Stop mode

The Stop mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 39 for more details on how to exit from Stop mode.

When exiting from Stop mode, the system clock, D3 domain bus matrix clocks and voltage scaling are reset.

STOPF status flag in PWR CPU control register (PWR_CPUCR) indicates that the system has exited from Stop mode (see Table 33 ).

I/O states in Stop mode

I/O pin configuration remain unchanged in Stop mode.

6.7.9 DStandby mode

Like DStop mode, DStandby mode is based on the CPU subsystem CStop mode. However the domain V _CORE supply is powered off. A domain enters DStandby mode only when the CPU subsystem is in CStop mode if peripherals are allocated in the domain

A domain enters DStandby mode only when the CPU subsystem is in CStop mode if peripherals are allocated in the domain and the PDDS_Dn bit in PWR CPU control register (PWR_CPUCR) for the domain is configured accordingly. In DStandby mode, the domain is powered down and the domain RAM and register contents are lost.

Entering DStandby mode

The DStandby mode is entered according to Section 6.7.3: Entering low-power modes , when the PDDS_Dn bit in PWR CPU control register (PWR_CPUCR) for the Dn domain selects Standby mode.

Refer to Table 40 for details on how to enter DStandby mode.

If Flash memory programming is ongoing, the DStandby mode entry is delayed until the memory access is finished.

If an access to the domain bus matrix is ongoing, the DStandby mode entry is delayed until the domain bus matrix access is finished.

Note: When the CPU sets the PDDS_D2 bit to select Standby mode, the D2 domain enters DStandby mode (the CPU has no allocated peripherals in the D2 domain).

Exiting from DStandby mode

The DStandby mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 40 for more details on how to exit from DStandby mode.

Note: When the D2 domain is in DStandby mode and the CPU sets the domain PDDS_D2 bit to select Stop mode, the D2 domain remains in DStandby mode. The D2 domain will only exit DStandby when the CPU allocates a peripheral in the D2 domain.

When exiting from DStandby mode, the domain CPU and peripherals are reset. However the state of the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling depends on the system mode:

• • When the system did not enter Stop mode, the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling are the same as when entering DStandby mode.
• • When the system has entered Stop or Standby mode, the CPU subsystem clocks, domain(s) bus matrix clocks and voltage scaling are reset.

When the D2 domain exits from DStandby mode due to the CPU subsystem (i.e when allocating a first peripheral or when peripherals are allocated in the D2 domain and the CPU subsystem exits from CStop mode), the CPU shall verify that the domain has exited from DStandby mode. To ensure correct operation, it is recommended to follow the sequence below:

1. 1. First check that the domain bus matrix clock is available. The domain bus matrix clock state can be checked in RCC_CR register:
   • – When RCC_DnCKRDY = 0, the domain bus matrix clock is stalled.
   • – If RCC_DnCKRDY = 1, the domain bus matrix clock is enabled.
2. 2. Then wait for the domain has exited from DStandby mode. To do this, check the SBF_Dn flag in PWR CPU control register (PWR_CPUCR) . The domain is powered and can be accessed only when SBF_Dn is cleared. Below an example of code:

Loop
  write PWR_SBF_Dn = 0 ; try to clear bit.
  read PWR_SBF_Dn
  While 1 ==> loop

Table 40. DStandby mode

6.7.10 Standby mode

The Standby mode allows achieving the lowest power consumption. Like Stop mode, it is based on CPU subsystem CStop mode. However the \( V_{CORE} \) supply regulator is powered off.

The system D3 domain enters Standby mode only when the D1 and D2 domain are in DStandby. When the system D3 domain enters Standby mode, the voltage regulator is disabled. The complete \( V_{CORE} \) domain is consequently powered off. The PLLs, HSI oscillator, CSI oscillator, HSI48 and the HSE oscillator are also switched off. SRAM and register contents are lost except for backup domain registers (RTC registers, RTC backup register and backup RAM), and Standby circuitry (see Section 6.4.4: Backup domain ).

In system Standby mode, the following features can be selected by programming individual control bits:

• • Independent watchdog (IWDG)
  The IWDG is started by programming its Key register or by hardware option. Once started, it cannot be stopped except by a reset (see Section 50.3 in Section 50: Independent watchdog (IWDG) ).
• • Real-time clock (RTC)
  This is configured via the RTCEN bit in the backup domain control register (RCC_BDCR).
• • Internal RC oscillator (LSI RC)
  This is configured by the LSION bit in the Control/status register (RCC_CSR).
• • External 32.768 kHz oscillator (LSE OSC)
  This is configured by the LSEON bit in the backup domain control register (RCC_BDCR).

Entering Standby mode

The Standby mode is entered according to Section 6.7.3: Entering low-power modes , when all PDDS_Dn bits in PWR CPU control register (PWR_CPUCR) for all domains request Standby.

Refer to Table 42 for more details on how to enter to Standby mode.

Exiting from Standby mode

The Standby mode is exited according to Section 6.7.4: Exiting from low-power modes .

Refer to Table 42 for more details on how to exit from Standby mode.

The system exits from Standby mode when an external Reset (NRST pin), an IWDG Reset, a WKUP pin event, a RTC alarm, a tamper event, or a time stamp event is detected. All registers are reset after waking up from Standby except for power control and status registers ( PWR control register 2 (PWR_CR2) , PWR control register 3 (PWR_CR3) ), SBF bit in PWR CPU control register (PWR_CPUCR) , PWR wakeup flag register (PWR_WKUPFR) , and PWR wakeup enable and polarity register (PWR_WKUPEPR) .

After waking up from Standby mode, the program execution restarts in the same way as after a system reset (boot option sampling, boot vector reset fetched, etc.). The SBF status flags in PWR CPU control register (PWR_CPUCR) registers indicate from which mode the system has exited (see Table 41 ).

Table 41. Standby and Stop flags

1. When exiting from Standby the SBF_D1 and SBF_D2 reflect the reset value

Table 42. Standby mode

I/O states in Standby mode

In Standby mode, all I/O pins are high impedance without pull, except for:

• • Reset pad (still available)
• • RTC_AF1 pin if configured for tamper, time stamp, RTC Alarm out, or RTC clock calibration out
• • WKUP pins (if enabled). The WKUP pin pull configuration can be defined through WKUPPUPD register bits in PWR wakeup enable and polarity register (PWR_WKUPEPR) .

6.7.11 Monitoring low-power modes

The devices feature state monitoring pins to monitor the CPU and Domain state transition to low-power mode (refer to Table 43 for the list of pins and their description). The GPIO pin corresponding to each monitoring signal has to be programmed in alternate function mode.

This feature is not available in Standby mode since these I/O pins are switched to high impedance.

Table 43. Low-power modes monitoring pin overview

The values of the monitoring pins reflect the state of the CPU and domains. Refer to Table 44 for the GPIO state depending on CPU and domain state.

Table 44. GPIO state according to CPU and domain state

1. The full domain is in power off state and the CPU is powered off.

6.8 PWR registers

The PWR registers can be accessed in word, half-word and byte format, unless otherwise specified.

6.8.1 PWR control register 1 (PWR_CR1)

Address offset: 0x000

Reset value: 0xF000 C000

Bits 31:19 Reserved, must be kept at reset value.

Bits 18:17 ALS[1:0] : Analog voltage detector level selection

These bits select the voltage threshold detected by the AVD.

• 00: 1.7 V
• 01: 2.1 V
• 10: 2.5 V
• 11: 2.8 V

Bit 16 AVDEN : Peripheral voltage monitor on \( V_{DDA} \) enable

• 0: Peripheral voltage monitor on \( V_{DDA} \) disabled.
• 1: Peripheral voltage monitor on \( V_{DDA} \) enabled

Bits 15:14 SVOS[1:0] : System Stop mode voltage scaling selection

These bits control the \( V_{CORE} \) voltage level in system Stop mode, to obtain the best trade-off between power consumption and performance.

• 00: Reserved
• 01: SVOS5 Scale 5
• 10: SVOS4 Scale 4
• 11: SVOS3 Scale 3 (default)

Bits 13:10 Reserved, must be kept at reset value.

Bit 9 FLPS : Flash low-power mode in DStop mode

This bit allows to obtain the best trade-off between low-power consumption and restart time when exiting from DStop mode.

When it is set, the Flash memory enters low-power mode when D1 domain is in DStop mode.

• 0: Flash memory remains in normal mode when D1 domain enters DStop (quick restart time).
• 1: Flash memory enters low-power mode when D1 domain enters DStop mode (low-power consumption).

Bit 8 DBP : Disable backup domain write protection

In reset state, the RCC_BDCR register, the RTC registers (including the backup registers), BREN and MOEN bits in PWR_CR2 register, are protected against parasitic write access. This bit must be set to enable write access to these registers.

0: Access to RTC, RTC backup registers and backup SRAM disabled

1: Access to RTC, RTC backup registers and backup SRAM enabled

Note: Depending on the APB1 prescaler, there is a delay between the write to DBP and the effective disable/enable of the backup domain protection. Therefore, a dummy read operation to PWR_CR1 register is required just after writing to the DBP bit.

Bits 7:5 PLS[2:0] : Programmable voltage detector level selection

These bits select the voltage threshold detected by the PVD.

000: 1.95 V

001: 2.1 V

010: 2.25 V

011: 2.4 V

100: 2.55 V

101: 2.7 V

110: 2.85 V

111: External voltage level on PVD_IN pin, compared to internal V _REFINT level.

Note: Refer to Section “Electrical characteristics” of the product datasheet for more details.

Bit 4 PVDE : Programmable voltage detector enable

0: Programmable voltage detector disabled.

1: Programmable voltage detector enabled

Bits 3:1 Reserved, must be kept at reset value.

Bit 0 LPDS : Low-power DeepSleep with SVOS3 (SVOS4 and SVOS5 always use low-power, regardless of the setting of this bit)

0: Voltage regulator or SMPS step-down converter in Main mode (MR) when SVOS3 is selected for Stop mode

1: Voltage regulator or SMPS step-down converter in Low-power mode (LPR) when SVOS3 is selected for Stop mode

6.8.2 PWR control status register 1 (PWR_CSR1)

Address offset: 0x004

Reset value: 0x0000 4000

Bits 31:17 Reserved, must be kept at reset value.

Bit 16 AVDO : Analog voltage detector output on \( V_{DDA} \)

This bit is set and cleared by hardware. It is valid only if AVD on \( V_{DDA} \) is enabled by the AVDEN bit.

0: \( V_{DDA} \) is equal or higher than the AVD threshold selected with the ALS[2:0] bits.

1: \( V_{DDA} \) is lower than the AVD threshold selected with the ALS[2:0] bits

Note: Since the AVD is disabled in Standby mode, this bit is equal to 0 after Standby or reset until the AVDEN bit is set.

Bits 15:14 ACTVOS[1:0] : VOS currently applied for \( V_{CORE} \) voltage scaling selection.

These bits reflect the last VOS value applied to the PMU.

Bit 13 ACTVOSRDY : Voltage levels ready bit for currently used VOS and SDLEVEL

This bit is set to 1 by hardware when the voltage regulator and the SMPS step-down converter are both disabled and Bypass mode is selected in PWR control register 3 (PWR_CR3).

0: Voltage level invalid, above or below current VOS and SDLEVEL selected levels.

1: Voltage level valid, at current VOS and SDLEVEL selected levels.

Bits 12:5 Reserved, must be kept at reset value.

Bit 4 PVDO : Programmable voltage detect output

This bit is set and cleared by hardware. It is valid only if the PVD has been enabled by the PVDE bit.

0: \( V_{DD} \) or \( PVD\_IN \) voltage is equal or higher than the PVD threshold selected through the PLS[2:0] bits.

1: \( V_{DD} \) or \( PVD\_IN \) voltage is lower than the PVD threshold selected through the PLS[2:0] bits.

Note: since the PVD is disabled in Standby mode, this bit is equal to 0 after Standby or reset until the PVDE bit is set.

Bits 3:0 Reserved, must be kept at reset value.

6.8.3 PWR control register 2 (PWR_CR2)

Address offset: 0x008

Reset value: 0x0000 0000

This register is not reset by wakeup from Standby mode, RESET signal and \( V_{DD} \) POR. It is only reset by \( V_{SW} \) POR and VSWRST reset.

This register must not be accessed when VSWRST bit in RCC_BDCR register resets the \( V_{SW} \) domain.

After reset, PWR_CR2 register is write-protected. Prior to modifying its content, the DBP bit in PWR_CR1 register must be set to disable the write protection.

Bits 31:24 Reserved, must be kept at reset value.

Bit 23 TEMPH : Temperature level monitoring versus high threshold

0: Temperature below high threshold level.

1: Temperature equal or above high threshold level.

Bit 22 TEMPL : Temperature level monitoring versus low threshold

0: Temperature above low threshold level.

1: Temperature equal or below low threshold level.

Bit 21 VBATH : \( V_{BAT} \) level monitoring versus high threshold

0: \( V_{BAT} \) level below high threshold level.

1: \( V_{BAT} \) level equal or above high threshold level.

Bit 20 VBATL : \( V_{BAT} \) level monitoring versus low threshold

0: \( V_{BAT} \) level above low threshold level.

1: \( V_{BAT} \) level equal or below low threshold level.

Bits 19:17 Reserved, must be kept at reset value.

Bit 16 BRRDY : Backup regulator ready

This bit is set by hardware to indicate that the backup regulator is ready.

0: Backup regulator not ready.

1: Backup regulator ready.

Bits 15:5 Reserved, must be kept at reset value.

Bit 4 MONEN : V _BAT and temperature monitoring enable

When set, the V _BAT supply and temperature monitoring is enabled.

0: V _BAT and temperature monitoring disabled.

1: V _BAT and temperature monitoring enabled.

Note: V _BAT and temperature monitoring are only available when the backup regulator is enabled (BREN bit set to 1).

Bits 3:1 Reserved, must be kept at reset value.

Bit 0 BREN : Backup regulator enable

When set, the backup regulator (used to maintain the backup RAM content in Standby and V _BAT modes) is enabled.

If BREN is reset, the backup regulator is switched off. The backup RAM can still be used in Run and Stop modes. However, its content will be lost in Standby and V _BAT modes.

If BREN is set, the application must wait till the backup regulator ready flag (BRRDY) is set to indicate that the data written into the SRAM will be maintained in Standby and V _BAT modes.

0: Backup regulator disabled.

1: Backup regulator enabled.

6.8.4 PWR control register 3 (PWR_CR3)

Address offset: 0x00C

Reset value: 0x0000 0046

This register is reset only by a power-on reset (POR). It is not reset by a wakeup from Standby mode or a the RESET signal.

The lower byte of this register is written once after POR and must be written before changing VOS level or ck_sys clock frequency. No limitation applies to the upper bytes.

Programming data corresponding to an invalid combination of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS bits (see Table 30 ) will be ignored: data will not be written, the written-once mechanism will lock the register and any further write access will be ignored.

The default supply configuration will be kept and the ACTVOSRDY bit in PWR control status register 1 (PWR_CSR1) will go on indicating invalid voltage levels. The system must be power cycled before writing a new value.

Bits 31:27 Reserved, must be kept at reset value.

Bit 26 USB33RDY : USB supply ready.
0: USB33 supply not ready.
1: USB33 supply ready.

Bit 25 USBREGEN : USB regulator enable.
0: USB regulator disabled.
1: USB regulator enabled.

Bit 24 USB33DEN : \( V_{DD33USB} \) voltage level detector enable.
0: \( V_{DD33USB} \) voltage level detector disabled.
1: \( V_{DD33USB} \) voltage level detector enabled.

Bits 23:17 Reserved, must be kept at reset value.

Bit 16 SDEXTRDY : SMPS step-down converter external supply ready

This bit is set by hardware to indicate that the external supply from the SMPS step-down converter is ready.
0: External supply not ready.
1: External supply ready.

Bits 15:10 Reserved, must be kept at reset value.

Bit 9 VBRS : \( V_{BAT} \) charging resistor selection
0: Charge \( V_{BAT} \) through a 5 k \( \Omega \) resistor.
1: Charge \( V_{BAT} \) through a 1.5 k \( \Omega \) resistor.

Bit 8 VBE : \( V_{BAT} \) charging enable
0: \( V_{BAT} \) battery charging disabled.
1: \( V_{BAT} \) battery charging enabled.

Bits 7:6 Reserved, must be kept at reset value.

Bits 5:4 SDLEVEL[1:0] : SMPS step-down converter voltage output level selection

This bit is used when both the LDO and SMPS step-down converter are enabled with SDEN and LDOEN enabled or when SDEXTHP is enabled. In this case SDLEVEL has to be written with a value different than 00 at system startup.
00: Reset value
01: 1.8 V
10 and 11: 2.5 V

Note: Illegal combinations of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS are described in Table 30 .

Bit 3 SDEXTHP : SMPS step-down converter forced ON and in High Power MR mode.

0: SMPS step-down converter in normal operating mode.

1: SMPS step-down converter forced ON and in MR mode.

Note: Illegal combinations of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS are described in Table 30.

Bit 2 SDEN : SMPS step-down converter enable

0: SMPS step-down converter disabled

1: SMPS step-down converter enabled. (Default)

Note: Illegal combinations of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS are described in Table 30.

The SMPS step-down converter is not available on all packages. In this case, the SMPS step-down converter is disabled.

Bit 1 LDOEN : Low drop-out regulator enable

0: Low drop-out regulator disabled.

1: Low drop-out regulator enabled (default)

Note: Illegal combinations of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS are described in Table 30.

Bit 0 BYPASS : Power management unit bypass

0: Power management unit normal operation.

1: Power management unit bypassed, voltage monitoring still active.

Note: Illegal combinations of SDLEVEL, SDEXTHP, SDEN, LDOEN and BYPASS are described in Table 30.

6.8.5 PWR CPU control register (PWR_CPUCR)

This register allows controlling the CPU power.

Address offset: 0x010

Reset value: 0x0000 0000

Bits 31:12 Reserved, must be kept at reset value.

Bit 11 RUN_D3 : Keep system D3 domain in Run mode regardless of the CPU subsystems modes

0: D3 domain follows CPU subsystems modes.

1: D3 domain remains in Run mode regardless of CPU subsystems modes.

Bit 10 Reserved, must be kept at reset value.

Bit 9 CSSF : Clear D1 domain CPU Standby, Stop and HOLD flags (always read as 0)

This bit is cleared to 0 by hardware.

0: No effect.

1: D1 domain CPU flags (HOLD2F, STOPF, SBF, SBF_D1, and SBF_D2) are cleared.

This bit is set by hardware and cleared by any system reset or by setting the CPU CSSF bit. Once set, this bit can be cleared only when the D2 domain is no longer in DStandby mode.

0: D2 domain has not been in DStandby mode

1: D2 domain has been in DStandby mode.

This bit is set by hardware and cleared by any system reset or by setting the CPU CSSF bit. Once set, this bit can be cleared only when the D1 domain is no longer in DStandby mode.

0: D1 domain has not been in DStandby mode

1: D1 domain has been in DStandby mode.

This bit is set by hardware and cleared only by a POR (Power-on Reset) or by setting the CPU CSSF bit

0: System has not been in Standby mode

1: System has been in Standby mode

This bit is set by hardware and cleared only by any reset or by setting the CPU CSSF bit.

0: System has not been in Stop mode

1: System has been in Stop mode

Bits 4:3 Reserved, must be kept at reset value.

This bit allows CPU to define the Deepsleep mode for System D3 domain.

0: Keep Stop mode when D3 domain enters Deepsleep.

1: Allow Standby mode when D3 domain enters Deepsleep.

This bit allows CPU to define the Deepsleep mode for D2 domain.

0: Keep DStop mode when D2 domain enters Deepsleep.

1: Allow DStandby mode when D2 domain enters Deepsleep.

This bit allows CPU to define the Deepsleep mode for D1 domain.

0: Keep DStop mode when D1 domain enters Deepsleep.

1: Allow DStandby mode when D1 domain enters Deepsleep.

6.8.6 PWR D3 domain control register (PWR_D3CR)

This register allows controlling D3 domain power.

Address offset: 0x018

Reset value: 0x0000 4000 (after power up; 0x0000 6000 when regulator is correctly configured and for subsequent resets)

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:14 VOS[1:0] : Voltage scaling selection according to performance

These bits control the \( V_{CORE} \) voltage level and allow to obtain the best trade-off between power consumption and performance:

• – When increasing the performance, the voltage scaling must be changed before increasing the system frequency.
• – When decreasing performance, the system frequency must first be decreased before changing the voltage scaling.

00: Scale 0

01: Scale 3 (default)

10: Scale 2

11: Scale 1

Bit 13 VOSRDY : VOS Ready bit for \( V_{CORE} \) voltage scaling output selection.

When an internal regulator is used, this bit indicates that all the features allowed by the selected VOS can be used.

When VOS0 voltage scaling is selected, to guarantee that the clock frequency can be increased above the currently used maximum frequency, ACTVOS[1:0] must be equal to VOS[1:0] and ACTVOSRDY must be set.

Note: When Bypass mode is selected in the PWR control register 3 (PWR_CR3), VOSRDY bit is set to 1 by hardware whatever the \( V_{CORE} \) level.

0: Not ready, voltage level below VOS selected level.

1: Ready, voltage level at or above VOS selected level.

Bits 12:0 Reserved, must be kept at reset value.

6.8.7 PWR wakeup clear register (PWR_WKUPCR)

Address offset: 0x020

Reset value: 0x0000 0000 (reset only by system reset, not reset by wakeup from Standby mode)

5 wait states are required when writing this register (when clearing a WKUPF bit in PWR_WKUPFR, the AHB write access will complete after the WKUPF has been cleared).

Bits 31:6, 4, 2 Reserved, must be kept at reset value.

Bits 5, 3, 1:0 WKUPC[6, 4, 2:1] : Clear Wakeup pin flag for WKUPn, (n = 6, 4, 2, 1)

These bits are always read as 0.

0: No effect

1: Writing 1 clears the WKUPFn Wakeup pin flag (bit is cleared to 0 by hardware)

6.8.8 PWR wakeup flag register (PWR_WKUPFR)

Address offset: 0x024

Reset value: 0x0000 0000 (reset only by system reset, not reset by wakeup from Standby mode)

Bits 31:6, 4, 2 Reserved, must be kept at reset value.

Bits 5, 3, 1:0 WKUPF[6, 4, 2:1] : Wakeup pin WKUPn flag, (n = 6, 4, 2, 1)

This bit is set by hardware and cleared only by a Reset pin or by setting the WKUPCn bit in the PWR wakeup clear register (PWR_WKUPCR) .

0: No wakeup event occurred

1: A wakeup event was received from WKUPn pin

6.8.9 PWR wakeup enable and polarity register (PWR_WKUPEPR)

Address offset: 0x028

Reset value: 0x0000 0000 (reset only by system reset, not reset by wakeup from Standby mode)

Bits 31:28, 25:24, 21:20 Reserved, must be kept at reset value.

Bits 27:26, 23:22, 19:16 WKUPPUPD[6, 4, 2:1][1:0] : Wakeup pin pull configuration for WKUPn, (n = 6, 4, 2, 1)
These bits define the I/O pad pull configuration used when WKUPENn = 1. The associated GPIO port pull configuration must be set to the same value or to 00.
The Wakeup pin pull configuration is kept in Standby mode.
00: No pull-up
01: Pull-up
10: Pull-down
11: Reserved

Bits 15:14 Reserved, must be kept at reset value.

Bits 13, 11, 9:8 WKUPP[6, 4, 2:1] : Wakeup pin polarity bit for WKUPn, (n = 6, 4, 2, 1)
These bits define the polarity used for event detection on WKUPn external wakeup pin.
0: Detection on high level (rising edge)
1: Detection on low level (falling edge)

Bits 12, 10, 7:6 Reserved, must be kept at reset value.

Bits 5, 3, 1:0 WKUPEN[6, 4, 2:1] : Enable Wakeup Pin WKUPn, (n = 6, 4, 2, 1)
Each bit is set and cleared by software.
0: An event on WKUPn pin does not wakeup the system from Standby mode.
1: A rising or falling edge on WKUPn pin wakes-up the system from Standby mode.

Note: An additional wakeup event is detected if WKUPn+1 pin is enabled (by setting the WKUPENn bit) when WKUPn pin level is already high when WKUPPn+1 selects rising edge, or low when WKUPPn selects falling edge.

6.8.10 PWR register map

Table 45. Power control register map and reset values

Refer to Section 2.3 on page 131 for the register boundary addresses.