AN3147 Datasheet, PDF (17/25 Pages) STMicroelectronics – Power management in STM8L and STM8AL

AN3147
Run and low power modes
4.7
Note:
4.7.1
4.7.2
Low power run mode
This mode is based on code execution from RAM, using a low speed clock source. The
main voltage regulator (MVR) is switched off and the low power voltage regulator (LPVR) is
used to supply the voltage to internal structures. The Flash memory is configured by
software in I_DDQ mode.
The ADC is not supported in this mode, as its clock source must have a minimum frequency
of 1 MHz.
No interrupt is allowed in this mode as the interrupt vectors are located in the Flash (which is
switched off). Consequently, all interrupts must be masked.
While using this mode, you have to switch from high speed clock sources to low speed clock
sources.
This mode is not available on the STM8L101xx devices.
Entering Low power run mode
This mode is entered by executing the following software sequence:
1. Switch off all unused peripherals, oscillators (except LSI or LSE) and analog blocks
2. Mask all interrupts
3. Jump to RAM
4. Switch system clock to LSI or LSE clock sources
5. Configure the Flash memory in I_DDQ mode by setting the EEPM bit in the FLASH_CR1
register
6. Add a software delay loop to make sure the Flash/Data EEPROM are off
7. Configure the ultralow power mode for the regulator by setting the REGOFF bit in the
CLK_REGCSR register (do not confuse with the ULP bit in the PWR_CSR2 which
configures the behavior of the internal reference voltage).
Steps 1 to 4 can be performed in any order.
Exiting Low power run mode
The only way to exit this mode is to follow these steps:
1. Switch on the main regulator by resetting the REGOFF bit in the CLK_REGCSR
register. The REGREADY flag in the CLK_REGCSR register is set when the regulator
is ready.
2. Switch on the Flash/Data EEPROM by resetting the EEPM bit in the FLASH_CR1
register. The EEREADY flag in the CLK_REGCSR register is set when the Flash/Data
EEPROM is ready.
3. Switch the clock to HSI (or HSE).
4. Reset interrupt mask.
5. Switch on what is necessary and jump to Flash/Data EEPROM if needed.
DocID17035 Rev 3
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