Analysis and arrangement of Zhilin STM32 program source code 04

1 Overview

   The STM32 timer has many functions and complex configurations. I don't know much about it now, so I'll learn while using it. There are two places where the timer is used on the Zhilin development board. One is the backlight power supply of the LCD, which requires the output of a certain PWM waveform for rectification and power supply; the other is used to control the speaker, which is also the clock pulse output.

   The first choice for the timer is counting or timing. I use timing here. The output mode can be the capture of the timer during input, or the setting of output when the comparison matches (this one is often used).

2. Source program

void TIMx_Config(void) {

 TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure; //Time base unit configuration data structure

 TIM_OCInitTypeDef  TIM_OCInitStructure; //Output mode setting data structure

 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2; //PA2, multiplexed output mode

 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  //For timing 2 channel 3

 GPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz;

 GPIO_Init(GPIOA, &GPIO_InitStructure);

 TIM_TimeBaseStructure.TIM_Period = CCR3_Val; //40 is written to the auto-load register, 150KHz output.

 TIM_TimeBaseStructure.TIM_Prescaler = 2; //Division factor 3

 TIM_TimeBaseStructure.TIM_ClockDivision = 0; // related to sampling, not used here

 //The characteristics of upward counting are: from 0 to the loaded value, an overflow occurs; then counting starts from 0 again.

 TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

 TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

 TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Toggle; //Timer count flips when it matches the comparison channel

 TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;  // Enable output channel

 TIM_OCInitStructure.TIM_Pulse = CCR3_Val; //Compare the count value of the channel

 TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low; //Low level is valid

 TIM_OC3Init(TIM2, &TIM_OCInitStructure);

 TIM_OC3PreloadConfig(TIM2, TIM_OCPreload_Enable);  //Automatically reload, preload

 TIM_Cmd(TIM2, ENABLE);  

//TIM_ITConfig(TIM2, TIM_IT_CC3, ENABLE);

}

Here only the output of timer 2 channel 3 used by the LCD is listed, and the output frequency is 150kHz. No interrupts are used. How is this frequency obtained? First, TIM2 uses APB1's 36M, and after pre-division, the division factor is (Prescaler+1)=3, and after 3 division, it is 12MHz. The counting cycle is 40, and the count to 40 matches the output compare register, triggering the output flip, and then the counter starts counting again. Therefore, the frequency of the output channel is 12MHz divided by 80, which is 150kHz.

2. Serial port configuration

It is not very convenient to input commands by keystrokes. Soon I will have to write a serial communication program to input commands through the serial port and control the development board. It is very convenient to use library functions for serial port configuration.

void UART_Config(void){  //Initialize the configuration of the serial port

 USART_InitTypeDef USART_InitStructure;

 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;  

 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

 GPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz;

 GPIO_Init(GPIOA, &GPIO_InitStructure);

 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;     

 USART1->BRR =0x0271;     

 USART_Cmd(USART1, ENABLE);    

}