Why can’t APB2 clock be set to 72MHz on STM32F103RB using STM32CubeMX?

[김형건]

Hi,

I am using the STM32F103RB (NUCLEO-F103RB) and trying to configure the clocks using STM32CubeMX.

According to the official reference manual (RM0008) and datasheet, the maximum allowed APB2 clock frequency is 72 MHz, and I know that peripherals like TIM1 or ADC are connected to APB2.

I have tried several combinations of PLL settings:

HSE = 8MHz

PLL Multiplier = x9 → SYSCLK = 72MHz

AHB Prescaler = /1

APB2 Prescaler = /1 (PCLK2 = SYSCLK = 72MHz)

However, in the CubeMX Clock Configuration tab, even when I do this, the APB2 clock (PCLK2) never goes above 64 MHz. CubeMX simply refuses to allow me to set it to 72MHz. It caps it at 64 MHz.

My questions are:
Is this a limitation of STM32CubeMX, or does STM32F103RB actually not support APB2 at 72MHz despite the datasheet?

If this is a CubeMX issue, is there a workaround or a manual fix for it?

How can I really run TIM1 or ADC at their maximum clock (72MHz) as stated in the datasheet?

I'd appreciate any clarification or feedback from ST engineers or other users who have faced this issue.

Thanks in advance!

[TDK · Accepted solution]

> HSE = 8MHz

> PLL Multiplier = x9 → SYSCLK = 72MHz

Works fine here.

Include your IOC if you're having issues. Ensure you're on the latest version of the software.