原创 STM32 USART1初始化函数，非使用STM32库方式。

//=============================================================================
//       USART1 72MHZ  USART2/3 36MHZ
//        9600波特率， 1个停止位，8个数据位，     偶校验
//2. 只有USART1使用PCLK2(最高72MHz)。其它USART使用PCLK1(最高36MHz)。
//=============================================================================
void STM32_USART_Configuration(void)
{

         //USART_InitTypeDef USART_InitStructure;
         //GPIO_InitTypeDef GPIO_InitStructure;

   /* GPIOA Periph clock enable */
   //RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO | RCC_APB2Periph_GPIOA, ENABLE);
 STM32_Rcc_Regs->apb2enr.all |=(RCC_IOPAEN|RCC_AFIOEN);   // 时钟使能

   /* USART1 Periph clock enable */
   //RCC_APB2PeriphClockCmd(RCC_APB1Periph_USART1, ENABLE);
 STM32_Rcc_Regs->apb2enr.all|=RCC_USART1EN;    // USART1时钟使能
 STM32_Rcc_Regs->apb2enr.bit.USART1EN=1;    // USART1时钟使能

        /* Configure USART1 Tx (PA.09) as alternate function push-pull */
        //GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
        //GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
        //GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
        //GPIO_Init(GPIOA, &GPIO_InitStructure);

 STM32_Gpioa_Regs->crh.bit.CNF9=Output_Af_push_pull;    // 2
 STM32_Gpioa_Regs->crh.bit.MODE9=Output_Mode_50mhz;      // 2

        /* Configure USART1 Rx (PA.10) as input floating */
        //GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
        //GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
        //GPIO_Init(GPIOA, &GPIO_InitStructure);

 STM32_Gpioa_Regs->crh.bit.CNF10=Input_floating;     // 1
 STM32_Gpioa_Regs->crh.bit.MODE10=Input_Mode;        // 0

   // USART1_DeInit(USART1);
   STM32_Rcc_Regs->apb2rstr.all |=  RCC_USART1RST;// usart1 复位
   STM32_Rcc_Regs->apb2rstr.all &= ~RCC_USART1RST;
 
/*
        USART_InitStructure.USART_BaudRate =9600;
        USART_InitStructure.USART_WordLength = USART_WordLength_8b;
        USART_InitStructure.USART_StopBits = USART_StopBits_1;
        USART_InitStructure.USART_Parity = USART_Parity_No;
        USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
        USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
        USART_InitStructure.USART_Clock = USART_Clock_Disable;
        USART_InitStructure.USART_CPOL = USART_CPOL_Low;
        USART_InitStructure.USART_CPHA = USART_CPHA_2Edge;
        USART_InitStructure.USART_LastBit = USART_LastBit_Disable;
        // Configure USART1
        USART_Init(USART1, &USART_InitStructure);
*/

 STM32_Usart1_Regs->cr2.bit.STOP=0;// 00：1个停止位
 STM32_Usart1_Regs->cr2.bit.CLKEN=0;//
 STM32_Usart1_Regs->cr2.bit.LBCL=0;// 
 STM32_Usart1_Regs->cr2.bit.CPOL=0;//
 STM32_Usart1_Regs->cr2.bit.CPHA=1;//1：时钟第二个边沿进行数据捕获
 
        STM32_Usart1_Regs->cr1.bit.M=1;   // 字长   0:8数据位 ; 1：9个数据位
        STM32_Usart1_Regs->cr1.bit.PCE=1; //  0：校验控制被禁止1：校验控制被使能 
        STM32_Usart1_Regs->cr1.bit.PS=0;  // 0:偶校   EVEN
        STM32_Usart1_Regs->cr1.bit.TE=1;  // 1：发送被使能
        STM32_Usart1_Regs->cr1.bit.RE=1;  // 1：接收被使能

        STM32_Usart1_Regs->cr3.bit.RTSE=0; //RTS硬件流控制被禁止
        STM32_Usart1_Regs->cr3.bit.CTSE=0; //CTS硬件流控制被禁止
        STM32_Usart1_Regs->cr3.bit.SCEN=0; //1：智能卡模式被禁止   ?***
        // USARTDIV="72",000,000/(16*9600)=467.75=(467<<1)+(0.75*16)=1D40+0XC=1D4C
        STM32_Usart1_Regs->brr.all=0x1d4c; // 9600波特率的分频

        /* Enable USART1 Receive and Transmit interrupts */
        //USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
        //USART_ITConfig(USART1, USART_IT_TXE, ENABLE);
 STM32_Usart1_Regs->cr1.bit.RXNEIE=0;//接收缓冲区非空中断使能 1：当USART_SR中的ORE或者RXNE为1时，产生USART中断
        STM32_Usart1_Regs->cr1.bit.TXEIE=0; // 发送缓冲区空中断使能 1：当USART_SR中的TXE为1时，产生USART中断

        /* Enable the USART1 */
       // USART_Cmd(USART1, ENABLE);
 STM32_Usart1_Regs->cr1.bit.UE=1;// 1：USART模块使能

 /* enabling interrupt  设置USART1中断优先级，和关中断*/
 STM32_Nvic_Regs->Priority[37].all=0x40;
 STM32_Nvic_Regs->Enable[1].bit.INT5=0;  // 37  (37-32=5)  44 可设置 USART1 USART1全局中断 0x0000_00D4

}//END SUB