DocID024130 Rev 2

7/22

AN4231

Low Power Modes overview

 Wakeup unit (WKPU)



8 KB of RAM



Real time clock/ Autonomous Periodic Interrupt (RTC_API)



CANSampler



Slow IRC



Fast IRC (can be optionally disabled)



System Status and Configuration Module (SSCM)

This mode is intended as follows:



As an extreme low-power mode with everything powered down apart from the

necessary circuitry to allow device wakeup and eventually a RTC/API (real time clock)

implementation



To be used by software to remain in the lowest power consumption state with no

requirement to wake up quickly

To exit from this mode, a wakeup event occurs. For this reason, the wake up unit is

configured before entering in the STANDBY mode.However, in addition to booting from the

default location, the microcontroller is also configured to boot from the backup RAM. In the

case of booting from backup RAM, it is also possible to keep the CFLASH and DFLASH

disable by writing “01” to the CFLAON and DFLAON field in the ME_DRUN_MC register

prior to STANDBY entry. This allows a lower power consumption and a faster wakeup time,

due to the fact that it does not need to wait for FLASH initialization (about ~120 us).

If there is a STANDBY mode request while any wakeup event is active, the microcontroller

does not enter STANDBY mode.

In STANDBY mode power domain 1 is disabled. Power domains 2 and 3 are selectively

configured to enable additional SRAM as defined in Figure 2.

For more information on the Low Power Management refer to the Chapter 11 of the RM.

1.1

Settings for RAM in STANDBY

STANDBY mode offers maximum power saving. The level of power saving is software-

controllable via the settings in the PCU_PCONFn registers for power domain 2 onwards.

Power domain 0 stays connected to the power supply while power domain 1 is disconnected

from the power supply.

Power domains 2 and 3 contain the backup RAM extensions and is only powered down

during STANDBY mode. Therefore, writing ‘0’ to the respective bits for the other modes do

not power down those domains.

Depending on PCONF[2-3] configuration, there are four possible combinations for the

amount of RAM active in STANDBY mode as shown in the Table 2. The 40 KB option results

in a non-contiguous address space.