stm32 /stm32h7rs /STM32H7R /RCC /RCC_PLL1FRACR

fractional part of the multiplication factor for PLL1 VCO Set and reset by software to control the fractional part of the multiplication factor of the VCO. These bits can be written at any time, allowing dynamic fine-tuning of the PLL1 VCO. The software must set correctly these bits to insure that the VCO output frequency is between its valid frequency range, that is: 128 to 544 MHz if PLL1VCOSEL = 0 150 to 420 MHz if PLL1VCOSEL = 1 VCO output frequency = F_{ref1_ck} x (DIVN1 + (FRACN / 2¹³)), with DIVN1 between 8 and 420 FRACN can be between 0 and 2¹³- 1 The input frequency F_{ref1_ck} must be between 1 and 16 MHz. To change the FRACN value on-the-fly even if the PLL is enabled, the application must proceed as follows: Set the bit PLL1FRACLE to 0. Write the new fractional value into FRACN. Set the bit PLL1FRACLE to 1.