如何在keil5的环境下编写stm32的串口通讯代码，请编写它的.c文件与.h文件

下面是一个简单的示例，展示如何在Keil5环境下编写基本的STM32串口通讯代码。这里使用的是STM32F4系列的芯片，但是代码可以根据不同的芯片进行修改。

### .h文件

#ifndef __USART_H
#define __USART_H

#include "stm32f4xx.h"
#include <stdio.h>

#define USARTx                           USART2
#define USARTx_CLK                       RCC_APB1Periph_USART2
#define USARTx_CLK_INIT                  RCC_APB1PeriphClockCmd
#define USARTx_IRQn                      USART2_IRQn
#define USARTx_IRQHandler                USART2_IRQHandler

#define USARTx_TX_PIN                    GPIO_Pin_2
#define USARTx_TX_GPIO_PORT              GPIOD
#define USARTx_TX_GPIO_CLK               RCC_AHB1Periph_GPIOD
#define USARTx_TX_SOURCE                 GPIO_PinSource2
#define USARTx_TX_AF                     GPIO_AF_USART2

#define USARTx_RX_PIN                    GPIO_Pin_3
#define USARTx_RX_GPIO_PORT              GPIOD
#define USARTx_RX_GPIO_CLK               RCC_AHB1Periph_GPIOD
#define USARTx_RX_SOURCE                 GPIO_PinSource3
#define USARTx_RX_AF                     GPIO_AF_USART2

#define USARTx_BAUDRATE                  115200

void USART_Config(void);
void USART_SendChar(char data);
void USART_SendString(char *string);
int fputc(int ch, FILE *f);

#endif /* __USART_H */

### .c文件

#include "usart.h"

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

  /* Enable GPIO clock */
  RCC_AHB1PeriphClockCmd(USARTx_TX_GPIO_CLK | USARTx_RX_GPIO_CLK, ENABLE);

  /* Enable USART clock */
  USARTx_CLK_INIT(USARTx_CLK, ENABLE);

  /* Connect USART pins to AF7 */
  GPIO_PinAFConfig(USARTx_TX_GPIO_PORT, USARTx_TX_SOURCE, USARTx_TX_AF);
  GPIO_PinAFConfig(USARTx_RX_GPIO_PORT, USARTx_RX_SOURCE, USARTx_RX_AF);

  /* Configure USART TX and RX pins */
  GPIO_InitStructure.GPIO_Pin = USARTx_TX_PIN | USARTx_RX_PIN;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
  GPIO_Init(GPIOD, &GPIO_InitStructure);

  /* Configure USART */
  USART_InitStructure.USART_BaudRate = USARTx_BAUDRATE;
  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_Tx | USART_Mode_Rx;
  USART_Init(USARTx, &USART_InitStructure);

  /* Enable USART */
  USART_Cmd(USARTx, ENABLE);

  /* Configure USART interrupt */
  USART_ITConfig(USARTx, USART_IT_RXNE, ENABLE);

  /* Enable the USARTx Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = USARTx_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
}

void USART_SendChar(char data)
{
  while (USART_GetFlagStatus(USART