First of all, we confirm whether the output PWM pin is
PA6 TIM3 CH1 as output 1
PA7 TIM3 CH2 as output 2
or open the file of the 32 firmware library about PWM output. The
path is as follows
\STM32 firmware library v3.5\STM32F10x_StdPeriph_Lib_V3.5.0\Project\STM32F10x_StdPeriph_Examples\
Find the main function of TIM\PWM_Output and copy all the contents to the function
void TIM3_PWM_Init (void) we created
void TIM3_PWM_Init（void）{
}
Because the amount of code is too large to affect reading, so I will not post it
Then we copy the destructor name
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
Then we write the pre-split screen value
uint16_t PrescalerValue = 0;
Then the value of CCR1 is written
uint16_t CCR1_Val = 333;
Then we delete the functions configured
by the remaining CCR. The functions of the remaining CCR are as follows
/* PWM1 Mode configuration: Channel2 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR2_Val;
TIM_OC2Init(TIM3, &TIM_OCInitStructure);
TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel3 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR3_Val;
TIM_OC3Init(TIM3, &TIM_OCInitStructure);
TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);
/* PWM1 Mode configuration: Channel4 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR4_Val;
TIM_OC4Init(TIM3, &TIM_OCInitStructure);
TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Enable);
Then configure the two functions that we reported.
In fact, the firmware library uses function references.
We only need to replace the names of the corresponding function modules.
The first is the RCC file
void RCC_Configuration(void)
{
/* TIM3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB |
RCC_APB2Periph_GPIOC | RCC_APB2Periph_AFIO, ENABLE);
}
The PWM output we use is
TIM3 CCR2 corresponding to PA7 pin
TIM2 CCR2 corresponding to PA1 pin
So we only keep the TIM3 and PA ports and the multiplexed clock
/* TIM3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
Next is our GPIO pin IO port
. The configuration process is the same as before.
Find this code
/*GPIOB Configuration: TIM3 channel1, 2, 3 and 4 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7 | GPIO_Pin_8 | GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOC, &GPIO_InitStructure);
GPIO_PinRemapConfig(GPIO_FullRemap_TIM3, ENABLE);
Then just keep PA7
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
Next, we have configured the input and output of an IO port.
Next, let’s calculate the output PWM frequency.
Let’s take a look at this comment.
/* -----------------------------------------------------------------------
TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
clock at 24 MHz the Prescaler is computed as following:
- Prescaler = (TIM3CLK / TIM3 counter clock) - 1
SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
and Connectivity line devices and to 24 MHz for Low-Density Value line and
Medium-Density Value line devices
The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(ARR + 1)
= 24 MHz / 666 = 36 KHz
TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
----------------------------------------------------------------------- */
It says that he has decomposed 72Mhz into 24Mhz,
I guess it is this sentence
PrescalerValue = (uint16_t) (SystemCoreClock / 24000000) - 1;
The pre-allocation value is equal to the clock divided by 24000000-1
and then the clock is divided by the prescaler value
. The advantage of writing this way is that no matter how much your clock frequency is divided by this PrescalerValue, you
get 24Mhz
Then I saw that 24Mhz was broken down into 36KHz,
I guess it was this sentence.
TIM_TimeBaseStructure.TIM_Period = 665;
Set the cycle to 665 to complete one cycle and the frequency becomes 36KHz
. If we want to get 40KHz,
we need to calculate it in the reverse direction. 240 000 K/40K=600,
so we change it to
TIM_TimeBaseStructure.TIM_Period = 599;
So it should be possible to achieve a 40KHz square wave output for ultrasonic use. The
following is the complete code of the PWM configuration
#include "timer.h"
_Bool TIM2_led_flag =0;
u8 Tim2_conter =0;
void TIM2_Config(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStrure;
NVIC_InitTypeDef NVIC_InitStrure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
TIM_TimeBaseInitStrure.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseInitStrure.TIM_Period=1000;//¼ÆÊýµ½1000 µÈÓÚ³ËÒÔÁË1000
TIM_TimeBaseInitStrure.TIM_Prescaler= 71 ; //72HMz/72=1Mhz = 1 000 000
TIM_TimeBaseInitStrure.TIM_RepetitionCounter= 0; //Öظ´ÇëÇó¼ÆÊýÆ÷
TIM_TimeBaseInit(TIM2,&TIM_TimeBaseInitStrure);
TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE);
TIM_Cmd(TIM2,ENABLE);
NVIC_InitStrure.NVIC_IRQChannel=TIM2_IRQn;
NVIC_InitStrure.NVIC_IRQChannelCmd=ENABLE;
NVIC_InitStrure.NVIC_IRQChannelPreemptionPriority=0;
NVIC_InitStrure.NVIC_IRQChannelSubPriority=1;
NVIC_Init(&NVIC_InitStrure);
}
void TIM2_IRQHandler()
{
if(TIM_GetITStatus(TIM2,TIM_IT_Update)!=RESET)
{
Tim2_conter++;
TIM_ClearITPendingBit(TIM2,TIM_IT_Update);
if(Tim2_conter > 250)
{
Tim2_conter=0;
TIM2_led_flag = !TIM2_led_flag;
}
}
}
void TIM3_PWM_Init(void)
{
uint16_t PrescalerValue = 0;
uint16_t CCR1_Val = 333;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
/* System Clocks Configuration */
/* TIM3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
/* GPIO Configuration */
/*GPIOB Configuration: TIM3 channel1, 2, 3 and 4 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_PinRemapConfig(GPIO_FullRemap_TIM3, ENABLE);
/* -----------------------------------------------------------------------
TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
clock at 24 MHz the Prescaler is computed as following:
- Prescaler = (TIM3CLK / TIM3 counter clock) - 1
SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
and Connectivity line devices and to 24 MHz for Low-Density Value line and
Medium-Density Value line devices
The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(ARR + 1)
= 24 MHz / 666 = 36 KHz
TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
----------------------------------------------------------------------- */
/* Compute the prescaler value */
PrescalerValue = (uint16_t) (SystemCoreClock / 24000000) - 1;
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 599;
TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR1_Val;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC2Init(TIM3, &TIM_OCInitStructure);
TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3, ENABLE);
/* TIM3 enable counter */
TIM_Cmd(TIM3, ENABLE);
}
void TIM2_PWM_Init(void)
{
uint16_t PrescalerValue = 0;
uint16_t CCR1_Val = 300;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
/* System Clocks Configuration */
/* TIM2 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
/* GPIO Configuration */
/*GPIOB Configuration: TIM2 channel1, 2, 3 and 4 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_PinRemapConfig(GPIO_FullRemap_TIM2, ENABLE);
/* -----------------------------------------------------------------------
TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
clock at 24 MHz the Prescaler is computed as following:
- Prescaler = (TIM3CLK / TIM3 counter clock) - 1
SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
and Connectivity line devices and to 24 MHz for Low-Density Value line and
Medium-Density Value line devices
The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(ARR + 1)
= 24 MHz / 666 = 36 KHz
TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
----------------------------------------------------------------------- */
/* Compute the prescaler value */
PrescalerValue = (uint16_t) (SystemCoreClock / 24000000) - 1;
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 599;
TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR1_Val;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC2Init(TIM2, &TIM_OCInitStructure);
TIM_OC2PreloadConfig(TIM2, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM2, ENABLE);
/* TIM3 enable counter */
TIM_Cmd(TIM2, ENABLE);
}