STM32 uses IO port to simulate serial port

PB12 simulates TXD, and PB13 simulates RXD. The transmission timing is relatively simple, and can be realized quickly according to the timing diagram. The reception is more complicated. Here, the overflow interrupt of the timer TM4 and the external interrupt of the PB13 are used to calculate the level time to obtain the serial port data.

#define BuadRate_9600	100
u8 len = 0;	//接收计数
u8 USART_buf[11];  //接收缓冲区
#define OI_TXD	PBout(12)
#define OI_RXD	PBin(13)

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 rf315_IoConfig()
{
	GPIO_InitTypeDef  GPIO_InitStructure;
	NVIC_InitTypeDef NVIC_InitStructure;
 	EXTI_InitTypeDef EXTI_InitStruct;
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO|RCC_APB2Periph_GPIOB, ENABLE);	 //使能PB,PC端口时钟 
	 
	 //SoftWare Serial TXD
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12;	    
  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(GPIOB,GPIO_Pin_12); 						
	 
	 
	//SoftWare Serial RXD
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;		
	GPIO_Init(GPIOB, &GPIO_InitStructure);	 

	GPIO_EXTILineConfig(GPIO_PortSourceGPIOB, GPIO_PinSource13);
	EXTI_InitStruct.EXTI_Line = EXTI_Line13;
	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			 
}
void rf315_uart4Init()
{
	rf315_IoConfig();
	TIM4_Int_Init(107, 71);	 //1M计数频率
}

void rf315_SendChar(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 rf315_SendData(u8 *buf, u8 len)
{
	u8 t;
	for(t = 0; t < len; t++)
	{
		rf315_SendChar(buf[t]);
	}
}


void EXTI15_10_IRQHandler(void)
{
	if(EXTI_GetFlagStatus(EXTI_Line13) != RESET)
	{
		if(OI_RXD == 0) 
		{
			if(recvStat == COM_STOP_BIT)
			{
				recvStat = COM_START_BIT;
				TIM_Cmd(TIM4, ENABLE);
			}
		}
		EXTI_ClearITPendingBit(EXTI_Line13);
	}
}

u8 rf315_data_need_handler=0;

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;	
			/*数据协议尾*/
			if(USART_buf[len-1]==RF315_PROTOCOL_TAIL)
				rf315_data_need_handler=1;
			return;
		}
		if(OI_RXD)
		{
			recvData |= (1 << (recvStat - 1));
		}else{
			recvData &= ~(1 << (recvStat - 1));
		}	
  }		
}