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Timer 2 on STM32F401C Discovery Board

Question asked by deering.paul on Sep 10, 2015
Latest reply on Sep 10, 2015 by Clive One
Hi all,

I've just started playing with the STM32F4 on the STM32F401C Discovery board, and had some strange behaviour (slowed down time) when attempting to generate a 1ms TIM2 interrupt.

From the reference manual for the microcontroller, I have enabled HSE via SW in RCC_CR to give me a (supposedly) 8Mhz reference clock (external 8Mhz crystal) to drive the AHB bus.  Both AHB and APB1 prescalers are set at 0, so no clock division on the bus clocks.

From this, I assume that the clock driving the prescaler for TIM2 should be 8Mhz.  I have set the prescale for TIM2 at 7 (CK_CNT = CK_PSC / 8), which, presumably, should give me a 1Mhz clock driving the counter (CK_CNT = 1Mhz).  I have set ARR at 999, which I assumed would supply a 1ms interrupt.  This clearly isn't the case.

Am I misreading the the documentation?  Have I missed something?