STM32 IO模拟实现软件串口

最近项目中STM32的串口资源紧张，于是使用IO口进行模拟串口，现进行整理记录。

1. 实现思路

IO口模拟串口的思路也比较简单，一切按照串口协议进行操作即可。

对于发送，计算好不同波特率对应的延时时间进行数据发送。

对于接收，稍微复杂。通过外部中断检测接收管脚的下降沿，检测到起始信号后开启定时器，定时器按照波特率设定好时间，每隔一段时间进入定时器中断接收数据，完成一个字节后关闭定时器。

2. 测试Demo说明

• TXD : PC13
• RXD : PB14
• 波特率：9600 ，1-8-N

3. Demo功能

接收11个数据，然后把接收到的数据发送出去。

4. 程序实现

#define OI_TXD  PCout(13)
#define OI_RXD  PBin(14)

#define BuadRate_9600   100

u8 len = 0; //接收计数
u8 USART_buf[11];  //接收缓冲区

enum{
    COM_START_BIT,
    COM_D0_BIT,
    COM_D1_BIT,
    COM_D2_BIT,
    COM_D3_BIT,
    COM_D4_BIT,
    COM_D5_BIT,
    COM_D6_BIT,
    COM_D7_BIT,
    COM_STOP_BIT,
};

u8 recvStat = COM_STOP_BIT;
u8 recvData = 0;

void IO_TXD(u8 Data)
{
    u8 i = 0;
    OI_TXD = 0;  
    delay_us(BuadRate_9600);
    for(i = 0; i < 8; i++)
    {
        if(Data&0x01)
            OI_TXD = 1;  
        else
            OI_TXD = 0;     
        
        delay_us(BuadRate_9600);
        Data = Data>>1;
    }
    OI_TXD = 1;
    delay_us(BuadRate_9600);
}
    
void USART_Send(u8 *buf, u8 len)
{
    u8 t;
    for(t = 0; t < len; t++)
    {
        IO_TXD(buf[t]);
    }
}
    
 void IOConfig(void)
 {
    GPIO_InitTypeDef  GPIO_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;
    EXTI_InitTypeDef EXTI_InitStruct;
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO|RCC_APB2Periph_GPIOB|RCC_APB2Periph_GPIOC, ENABLE);     //使能PB,PC端口时钟 
     
     //SoftWare Serial TXD
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13;      
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;       //推挽输出
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;      //IO口速度为50MHz   
  GPIO_Init(GPIOC, &GPIO_InitStructure);                    
  GPIO_SetBits(GPIOC,GPIO_Pin_13);                      
     
     
    //SoftWare Serial RXD
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_14;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;     
    GPIO_Init(GPIOB, &GPIO_InitStructure);   

    GPIO_EXTILineConfig(GPIO_PortSourceGPIOB, GPIO_PinSource14);
    EXTI_InitStruct.EXTI_Line = EXTI_Line14;
    EXTI_InitStruct.EXTI_Mode=EXTI_Mode_Interrupt;
    EXTI_InitStruct.EXTI_Trigger=EXTI_Trigger_Falling; //下降沿触发中断
    EXTI_InitStruct.EXTI_LineCmd=ENABLE;
    EXTI_Init(&EXTI_InitStruct);


    NVIC_InitStructure.NVIC_IRQChannel= EXTI15_10_IRQn ; 
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=2; 
    NVIC_InitStructure.NVIC_IRQChannelSubPriority =2;  
    NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;  
    NVIC_Init(&NVIC_InitStructure);  
    
}
 
void TIM4_Int_Init(u16 arr,u16 psc)
{
  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE); //时钟使能
    
    //定时器TIM4初始化
    TIM_TimeBaseStructure.TIM_Period = arr; //设置在下一个更新事件装入活动的自动重装载寄存器周期的值   
    TIM_TimeBaseStructure.TIM_Prescaler =psc; //设置用来作为TIMx时钟频率除数的预分频值
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; //设置时钟分割:TDTS = Tck_tim
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上计数模式
    TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure); //根据指定的参数初始化TIMx的时间基数单位
    TIM_ClearITPendingBit(TIM4, TIM_FLAG_Update);
    TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE ); //使能指定的TIM3中断,允许更新中断

    //中断优先级NVIC设置
    NVIC_InitStructure.NVIC_IRQChannel = TIM4_IRQn;  //TIM4中断
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  //先占优先级1级
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;  //从优先级1级
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ通道被使能
    NVIC_Init(&NVIC_InitStructure);  //初始化NVIC寄存器            
}
 
 
 int main(void)
 {      
     NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);//设置中断优先级分组为组2：2位抢占优先级，2位响应优先级
     delay_init();
     IOConfig();
  TIM4_Int_Init(107, 71);    //1M计数频率
     
  while(1)
    {
        if(len > 10)
        {
            len = 0;
            USART_Send(USART_buf,11);
        }
    }
}

void EXTI15_10_IRQHandler(void)
{
    if(EXTI_GetFlagStatus(EXTI_Line14) != RESET)
    {
        if(OI_RXD == 0) 
        {
            if(recvStat == COM_STOP_BIT)
            {
                recvStat = COM_START_BIT;
                TIM_Cmd(TIM4, ENABLE);
            }
        }
        EXTI_ClearITPendingBit(EXTI_Line14);
    }
}

void TIM4_IRQHandler(void)
{  
    if(TIM_GetFlagStatus(TIM4, TIM_FLAG_Update) != RESET)
    {
        TIM_ClearITPendingBit(TIM4, TIM_FLAG_Update);   
         recvStat++;
        if(recvStat == COM_STOP_BIT)
        {
            TIM_Cmd(TIM4, DISABLE);
            USART_buf[len++] = recvData;    
            return;
        }
        if(OI_RXD)
        {
            recvData |= (1 << (recvStat - 1));
        }else{
            recvData &= ~(1 << (recvStat - 1));
        }   
  }     
}

5. Demo下载

Demo工程下载地址github。