Solved
Center aligned PWM is half the desired frequency
Posted on November 14, 2017 at 15:41
Hello everyone, I'm new to STM32 microcontrollers. I'm currently working on my first project using this microcontroller, it is for a motor control application. I am trying to set up the PWMs, I'd like to run them at a frequency of 15kHz and they must be center aligned. I am able to get edge aligned signals at this frequency, but when trying to set to center aligned the frequency drops to 58kHz. What am I doing wrong here?
/* Compute the value to be set in ARR register to generate signal frequency at 156 Khz */
TimerPeriod = (SystemCoreClock / 35156);
/* Compute CCR1 value to generate a duty cycle at 25% for channel 1 */
Channel1Pulse = (uint16_t) ((TimerPeriod + 1) - ((uint32_t) 25 * (TimerPeriod - 1)) / 1000);
/* Compute CCR2 value to generate a duty cycle at 25% for channel 2 */
Channel2Pulse = (uint16_t) ((TimerPeriod + 1) - ((uint32_t) 25 * (TimerPeriod - 1)) / 1000);
/* Compute CCR3 value to generate a duty cycle at 0% for channel 3 */
Channel3Pulse = (uint16_t) ((TimerPeriod + 1) - ((uint32_t) 25 * (TimerPeriod - 1)) / 1000);
/* Time Base configuration */
TIM_TimeBaseStructure.TIM_Prescaler = 0; /* Do not use a prescaler */
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_CenterAligned3; /* Timer mode: center aligned */
TIM_TimeBaseStructure.TIM_Period = TimerPeriod; /* Configure timer period to be TimerPeriod amount of clock ticks before an up count */
TIM_TimeBaseStructure.TIM_ClockDivision = 0; /* No clock division */
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
/* Channel 1, 2 and 3 Configuration in PWM mode */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; /* In upcounting, channel is inactive as long as TIMx_CNT<TIMx_CCR1 else active */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; /* OC1 signal is output on the corresponding output pin */
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable; /* OC1 signal is output on the corresponding output pin */
TIM_OCInitStructure.TIM_Pulse = Channel1Pulse; /* Value loaded in the actual capture/compare register (specifies when to assert active pulse) */
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; /* Sets PWM output to active high */
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High; /* Sets complimentary PWM output to active high */
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset; /* When idle, reset PWM output */
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Set; /* When idle, set PWM complimentary output */
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_Pulse = Channel2Pulse;
TIM_OC2Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_Pulse = Channel3Pulse;
TIM_OC3Init(TIM1, &TIM_OCInitStructure);
/* Automatic Output enable, Break, dead time and lock configuration*/
TIM_BDTRInitStructure.TIM_OSSRState = TIM_OSSRState_Enable; /* Off-State selection for Run Mode: When inactive, OC/OCN outputs are enabled with their inactive level as soon as CCxE=1 or CCxNE=1 */
TIM_BDTRInitStructure.TIM_OSSIState = TIM_OSSIState_Enable; /* Off-State selection for Idle Mode: When inactive, OC/OCN outputs are forced first with their idle level as soon as CCxE=1 or CCxNE=1 */
TIM_BDTRInitStructure.TIM_LOCKLevel = TIM_LOCKLevel_1; /* Bit write protection for DTG bits in TIMx_BDTR register, OISx and OISxN bits in TIMx_CR2 register and BKE/BKP/AOE bits in TIMx_BDTR register */
TIM_BDTRInitStructure.TIM_DeadTime = DEAD_TIME; /* Dead-time inserted between the complementary outputs */
TIM_BDTRInitStructure.TIM_Break = TIM_Break_Enable;
TIM_BDTRInitStructure.TIM_BreakPolarity = TIM_BreakPolarity_High;
TIM_BDTRInitStructure.TIM_AutomaticOutput = TIM_AutomaticOutput_Enable;
TIM_BDTRConfig(TIM1, &TIM_BDTRInitStructure);
/* TIM1 counter enable */
TIM_Cmd(TIM1, ENABLE);
/* Main Output Enable */
TIM_CtrlPWMOutputs(TIM1, ENABLE);�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?EDIT: Side question - what are the source code tags on this forum? The 'Source Code' button does not seem to do anything for me.
#center-aligned-pwm #stm32f3x-pwm #stm32f