stm32f107作为下位机，如何编写RS485通讯程序，写一段示例

下面是一个基本的STM32F107 RS485通讯程序示例：

#include "stm32f10x.h"
#include "stm32f10x_usart.h"
#include "stm32f10x_gpio.h"

#define USART1_DR_Base 0x40013804
#define MAX_BUFFER_SIZE 200

void GPIO_Configuration(void);
void USART1_Configuration(void);
void USART1_SendChar(uint16_t Data);
void USART1_SendString(uint8_t *str);
void USART1_IRQHandler(void);

uint8_t RxBuffer[MAX_BUFFER_SIZE];
volatile uint8_t RxCounter = 0;
volatile uint8_t RxFlag = 0;

int main(void)
{
    GPIO_Configuration();
    USART1_Configuration();
    while (1)
    {
        if (RxFlag)
        {
            USART1_SendString(RxBuffer);
            RxFlag = 0;
            RxCounter = 0;
        }
    }
}

void GPIO_Configuration(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

    //RS485 Driver Enable Pin
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_SetBits(GPIOA, GPIO_Pin_8);
}

void USART1_Configuration(void)
{
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA, ENABLE);

    //USART1_TX
    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);

    //USART1_RX
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    //USART1 Configuration
    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_Init(USART1, &USART_InitStructure);

    //USART1 Interrupt Configuration
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    USART_Cmd(USART1, ENABLE);
}

void USART1_SendChar(uint16_t Data)
{
    while (USART_GetFlagStatus(USART1, USART_FLAG_TC) == RESET);
    USART_SendData(USART1, Data);
}

void USART1_SendString(uint8_t *str)
{
    while (*str)
    {
        USART1_SendChar(*str++);
    }
}

void USART1_IRQHandler(void)
{
    if (USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
    {
        RxBuffer[RxCounter++] = USART_ReceiveData(USART1);
        if (RxCounter >= MAX_BUFFER_SIZE)
        {
            RxCounter = 0;
        }
        RxFlag = 1;
    }
}

这个程序设置了RS485驱动器的使能引脚和USART1串口的配置，并且实现了一个简单的接收中断程序。在主循环中，如果接收标志被触发，则发送接收缓冲区中的数据。