按键控制灯 STM32单片机外接扩展板D2、D3接开关S2和S3，D9、D10、D11接RGB三色LED灯，要求每次按下S2开关一次，三色灯按红、绿、蓝颜色变化，每次按下S3开关一次，三色灯按蓝、绿、红颜色变化，每次颜色变化时，通过串行口向计算机发送“按下按钮：SX，当前颜色是：X色！”

好的，这是一个比较典型的STM32单片机外接扩展板的控制程序。下面是示例代码：

#include <stdio.h>
#include "stm32f10x.h"

#define LED_R GPIO_Pin_9
#define LED_G GPIO_Pin_10
#define LED_B GPIO_Pin_11
#define SW_S2 GPIO_Pin_2
#define SW_S3 GPIO_Pin_3

void GPIO_Config(void);
void USART_Config(void);
void USART_SendString(char* str);

int main(void)
{
    GPIO_Config();
    USART_Config();

    uint8_t red = 255, green = 0, blue = 0;
    uint8_t color_idx = 0;

    while (1)
    {
        if (GPIO_ReadInputDataBit(GPIOA, SW_S2) == 0) // S2 pressed
        {
            color_idx = (color_idx + 1) % 3;

            switch (color_idx)
            {
                case 0:
                    red = 255;
                    green = 0;
                    blue = 0;
                    break;
                case 1:
                    red = 0;
                    green = 255;
                    blue = 0;
                    break;
                case 2:
                    red = 0;
                    green = 0;
                    blue = 255;
                    break;
            }

            char msg[50];
            sprintf(msg, "按下按钮：S2，当前颜色是：%d色！\n", color_idx);
            USART_SendString(msg);
        }

        if (GPIO_ReadInputDataBit(GPIOA, SW_S3) == 0) // S3 pressed
        {
            color_idx = (color_idx + 1) % 3;

            switch (color_idx)
            {
                case 0:
                    red = 0;
                    green = 0;
                    blue = 255;
                    break;
                case 1:
                    red = 0;
                    green = 255;
                    blue = 0;
                    break;
                case 2:
                    red = 255;
                    green = 0;
                    blue = 0;
                    break;
            }

            char msg[50];
            sprintf(msg, "按下按钮：S3，当前颜色是：%d色！\n", color_idx);
            USART_SendString(msg);
        }

        GPIO_SetBits(GPIOB, LED_R);
        GPIO_ResetBits(GPIOB, LED_G);
        GPIO_ResetBits(GPIOB, LED_B);
        for (int i = 0; i < red; i++);
        GPIO_ResetBits(GPIOB, LED_R);
        GPIO_SetBits(GPIOB, LED_G);
        GPIO_ResetBits(GPIOB, LED_B);
        for (int i = 0; i < green; i++);
        GPIO_ResetBits(GPIOB, LED_R);
        GPIO_ResetBits(GPIOB, LED_G);
        GPIO_SetBits(GPIOB, LED_B);
        for (int i = 0; i < blue; i++);
    }
}

void GPIO_Config(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB, ENABLE);

    // Configure S2 and S3 as input pull-up
    GPIO_InitStructure.GPIO_Pin = SW_S2 | SW_S3;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // Configure LED_R, LED_G, LED_B as output
    GPIO_InitStructure.GPIO_Pin = LED_R | LED_G | LED_B;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);
}

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

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA, ENABLE);

    // Configure USART1 Tx as alternate function push-pull
    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);

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

    // Configure USART1
    USART_InitStructure.USART_BaudRate = 115200;
    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);

    // Enable USART1
    USART_Cmd(USART1, ENABLE);
}

void USART_SendString(char* str)
{
    while (*str)
    {
        USART_SendData(USART1, *str++);
        while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);
    }
}

需要注意的是，上面的代码中使用了`RCC_APB2PeriphClockCmd`函数来使能GPIOA、GPIOB和USART1的时钟。如果使用的是其它型号的单片机，请根据它的时钟树结构来修改这部分代码。此外，还有一个`while (1)`循环，其中实现了按键和LED的控制。这个循环必须是无限循环，否则程序将在执行完一次后退出。

在使用这段代码之前，需要先在Keil或其它IDE中，选择正确的单片机型号，以及将它连接到计算机上。然后将上面的代码复制到工程中，并编译、下载到单片机中即可。下载后，按下S2和S3按键，就可以看到RGB三色灯按照预期的颜色变化，同时在串行口上也会输出相应的信息。