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STM32L1xx: why CubeMX alerts me APB1 frequency should be >= 10MHz ?

Question asked by Cesare Riva on May 30, 2018
Latest reply on May 30, 2018 by Cesare Riva

Good morning to everyone,

I am developing a low power application on STM32L151RET6, the clock is generated by MSI @4.194 MHz. In this configuration I am experiencing some strange behaviour when I use the ADC synched by Timer4, in fact the resulting sample frequency seems not correct and if I change the source clock from MSI to HSE+PLL @6MHz the ADC even doesn't start (no ADC callback is invoked).


If I configure the clock configuration using CubeMX (latest version 4.25.1) surprisingly it warns me that APB1 clock must be >= 10MHz.


If I look at the STM32L151RET datasheet, table 13, paragraph 6.3.1 (page 61, rev.9) the section "General operating conditions" reports that the min and max values of APB1 clock frequency should be from 0 to 32Mhz.


So, is there a real limitation on minimum APB1 clock frequency? I read again the STM32L1X Reference Manual but nothing I could find out more.


Thank you in advance.