设计一个简易的51单片机十字路口交通灯，要求一共12只LED发光二极管，红绿黄各4只，红灯时间为15秒，绿灯剩余15秒时转换为黄灯，附代码

好的，以下是一个简单的51单片机十字路口交通灯的程序，使用了12只LED发光二极管，红绿黄各4只，红灯时间为15秒，绿灯剩余15秒时转换为黄灯。

#include <reg51.h>

#define LED_RED1 P2_0
#define LED_YELLOW1 P2_1
#define LED_GREEN1 P2_2
#define LED_RED2 P2_3
#define LED_YELLOW2 P2_4
#define LED_GREEN2 P2_5
#define LED_RED3 P2_6
#define LED_YELLOW3 P2_7
#define LED_GREEN3 P3_0
#define LED_RED4 P3_1
#define LED_YELLOW4 P3_2
#define LED_GREEN4 P3_3

void delay(unsigned int time);

void main()
{
    while(1)
    {
        //第一组红灯亮
        LED_RED1 = 1;
        LED_GREEN2 = 1;
        LED_GREEN3 = 1;
        LED_RED4 = 1;
        delay(15000);

        //第一组绿灯亮
        LED_RED1 = 0;
        LED_YELLOW1 = 0;
        LED_GREEN1 = 1;
        delay(30000);

        //第一组黄灯亮
        LED_GREEN1 = 0;
        LED_YELLOW1 = 1;
        delay(5000);

        //第二组红灯亮
        LED_YELLOW1 = 0;
        LED_RED1 = 1;
        LED_GREEN1 = 0;
        LED_RED3 = 1;
        LED_YELLOW4 = 1;
        LED_GREEN4 = 0;
        delay(15000);

        //第二组绿灯亮
        LED_RED3 = 0;
        LED_YELLOW3 = 0;
        LED_GREEN3 = 1;
        delay(30000);

        //第二组黄灯亮
        LED_GREEN3 = 0;
        LED_YELLOW3 = 1;
        delay(5000);

        //第三组红灯亮
        LED_YELLOW3 = 0;
        LED_RED3 = 1;
        LED_GREEN3 = 0;
        LED_RED2 = 1;
        LED_YELLOW1 = 1;
        LED_GREEN1 = 0;
        delay(15000);

        //第三组绿灯亮
        LED_RED2 = 0;
        LED_YELLOW2 = 0;
        LED_GREEN2 = 1;
        delay(30000);

        //第三组黄灯亮
        LED_GREEN2 = 0;
        LED_YELLOW2 = 1;
        delay(5000);

        //第四组红灯亮
        LED_YELLOW2 = 0;
        LED_RED2 = 1;
        LED_GREEN2 = 0;
        LED_RED4 = 0;
        LED_YELLOW3 = 1;
        LED_GREEN3 = 0;
        delay(15000);

        //第四组绿灯亮
        LED_RED4 = 1;
        LED_YELLOW4 = 0;
        LED_GREEN4 = 1;
        delay(30000);

        //第四组黄灯亮
        LED_GREEN4 = 0;
        LED_YELLOW4 = 1;
        delay(5000);
    }
}

void delay(unsigned int time)
{
    unsigned int i, j;
    for(i = 0; i < time; i++)
        for(j = 0; j < 120; j++);
}

注意：该程序只是简单的实现了交通灯的功能，实际使用中还需要考虑其他因素，比如车辆的流量、行人的通行等，需要根据实际情况进行调整。