ST STM32G4 Series Reference Manual page 191

RM0440
The main regulator provides a typical output voltage at 1.0 V. The system clock frequency
can be up to 26 MHz.The Flash access time for a read access is increased as compared to
Range 1; write and erase operations are not possible.
Voltage scaling is selected through the VOS bit in the
(PWR_CR1)
The sequence to go from Range 1 (Normal/Boost) to Range 2 is:
1. In case of switching from Range 1 boost mode to Range 2, the system clock must be
divided by 2 using the AHB prescaler before switching to a lower system frequency for
at least 1us and then reconfigure the AHB prescaler.
2. Reduce the system frequency to a value lower than 26 MHz.
3. Adjust number of wait states according new frequency target in Range 2 (LATENCY
bits in the FLASH_ACR).
4. Program the VOS bits to "10" in the PWR_CR1 register.
The sequence to go from Range 2 to Range 1 (normal/boost mode) is:
1. 1. Program the VOS bits to "01" in the PWR_CR1 register.
2. Wait until the VOSF flag is cleared in the PWR_SR2 register.
3. Adjust number of wait states according new frequency target in Range 1 (LATENCY
bits in the FLASH_ACR).
4. Increase the system frequency by following below procedure:
•
If the system frequency is 26 MHz < SYSCLK ≤ 150 MHz:
–
–
•
If the system frequency is SYSCLK > 150 MHz:
–
–
–
–
The sequence to switch from Range1 normal mode to Range1 boost mode is:
1. The system clock must be divided by 2 using the AHB prescaler before switching to a
higher system frequency.
2. Clear the R1MODE bit is in the PWR_CR5 register.
3. Adjust the number of wait states according to the new frequency target in range1 boost
mode
4. Configure and switch to new system frequency.
5. Wait for at least 1 1us and then reconfigure the AHB prescaler to get the needed HCLK
clock frequency.
The sequence to switch from Range1 boost mode to Range1 normal mode is:
register.
Select the Range 1 normal mode by setting R1MODE bit in the PWR_CR5
register.
Configure and switch to PLL for a new system frequency.
The system clock must be divided by 2 using the AHB prescaler before switching
to a higher system frequency.
Select the Range 1 boost mode by clearing the R1MODE bit is in the PWR_CR5
register.
Configure and switch to PLL for a new system frequency.
Wait for at least 1us and then reconfigure the AHB prescaler to get the needed
HCLK clock frequency.
Section 5.4.1: Power control register 1
RM0440 Rev 1
Power control (PWR)
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