I am newbie of STM32 board. After yesterday I had tried a little experiment about timer. I use timer4 and use PLL clock as input source clock and finally in cubeMX, it said that APB is 32 MHz. My desire is I want to toggle pin every 500 ms and in configuration page I put pre-scaler to 32000 and count period is 499 so it should be interrupted every 500 ms after I programmed that on my STM32L053., timer gave an interrupt every 250 ms. I try to divide my pre-scaler by 2 and I got 500 ms. I had read a data sheet but still got nothing. I cannot figure out why the outcome turn in to this way. So is anyone know? what happened. Appreciated guys.