STM32F100 Timer-Clock

Posted on November 12, 2011 at 15:41

Hello forum!

I'm trying to get familiar with the timers in the STM32 but now I got stuck at a problem I can't solve, first here's the concerned function:

void TIM4_Configuration(void)

{

  /* Compute the prescaler value  -> @24MHz Prescaler = 0 */

  int PrescalerValue = (uint16_t) (SystemCoreClock / 24000000) - 1;

 

  /* Time base configuration */

  TIM_TimeBaseStructure.TIM_Period = 65535;

  TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;

  TIM_TimeBaseStructure.TIM_ClockDivision = 0;

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

 

  TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);

  /* TIM4 PWM2 Mode configuration: Channel1 */

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;

  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;

  TIM_OCInitStructure.TIM_Pulse = 15535;

  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

  TIM_OC1Init(TIM4, &TIM_OCInitStructure);

  TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);

  /* OPM Bit -> Only one pulse */

  TIM4->CR1 |= (1 << 3);

 

  /* TIM3 enable counter */

  TIM_Cmd(TIM4, ENABLE);

}

The purpose of this code is generating a pulse with a certain width ( TIMx_ARR - TIMx_CCR1 says the reference-manual, that means TIM_Period - TIM_Pulse using the library-structures , at least I think so :) ).

My problem now is that the pulse width is exact three times longer than the calculation says. A example how I calculated the pulse-width, so you can check if it's right :

SystemCoreClock = 24Mhz

TIM_Period = 65535

TIM_Pulse = 15535

(1 / SystemCoreClock) * (TIM_Period - TIM_Pulse) equals 2ms.

What am I missing?

Thank you in advance!

Chris

#timer-one-pulse