多机通信系统设计。 功能描述：一台主机，3台从机，从机地址分别为00H、01H、02H。对于主机，能够根据P1口的四位拨码开关的编程状态从3个从机中选择一个，读取P2开关的状态并从串口发送出去；对于从机，只有被选中的从机可以接收主机发送的开关状态，通过P2口的发光二极管显示；的C语言程序

以下是多机通信系统的C语言程序示例，包括主机和从机的程序：

主机程序：

#include <reg52.h>
#include <stdio.h>

#define BAUDRATE 9600
#define ADDR_00 0x00
#define ADDR_01 0x01
#define ADDR_02 0x02

sbit P1_0 = P1^0;
sbit P1_1 = P1^1;
sbit P1_2 = P1^2;
sbit P1_3 = P1^3;

sbit P2_0 = P2^0;
sbit P2_1 = P2^1;
sbit P2_2 = P2^2;
sbit P2_3 = P2^3;

unsigned char address;
unsigned char data;

void init_serial()
{
    TMOD |= 0x20;
    TH1 = 256 - (11059200/12/32/BAUDRATE);
    TL1 = TH1;
    TR1 = 1;
    SM0 = 0;
    SM1 = 1;
    REN = 1;
}

void send_data(unsigned char addr, unsigned char data)
{
    SBUF = addr;
    while(!TI);
    TI = 0;
    SBUF = data;
    while(!TI);
    TI = 0;
}

unsigned char read_switch()
{
    unsigned char value = 0;
    value |= P2_0 << 0;
    value |= P2_1 << 1;
    value |= P2_2 << 2;
    value |= P2_3 << 3;
    return value;
}

void main()
{
    init_serial();
    while(1)
    {
        if(P1_0 == 0)
            address = ADDR_00;
        else if(P1_1 == 0)
            address = ADDR_01;
        else if(P1_2 == 0)
            address = ADDR_02;
        else
            continue;

        data = read_switch();
        send_data(address, data);
    }
}

从机程序：

#include <reg52.h>
#include <stdio.h>

#define BAUDRATE 9600
#define ADDR_00 0x00
#define ADDR_01 0x01
#define ADDR_02 0x02

sbit P2_0 = P2^0;
sbit P2_1 = P2^1;
sbit P2_2 = P2^2;
sbit P2_3 = P2^3;

unsigned char address;
unsigned char data;

void init_serial()
{
    TMOD |= 0x20;
    TH1 = 256 - (11059200/12/32/BAUDRATE);
    TL1 = TH1;
    TR1 = 1;
    SM0 = 0;
    SM1 = 1;
    REN = 1;
}

void display_data(unsigned char data)
{
    P2_0 = data & 0x01;
    P2_1 = data & 0x02;
    P2_2 = data & 0x04;
    P2_3 = data & 0x08;
}

void main()
{
    init_serial();
    while(1)
    {
        if(RI)
        {
            address = SBUF;
            while(!TI);
            TI = 0;
            data = SBUF;
            while(!TI);
            TI = 0;

            if(address == ADDR_00 || address == ADDR_01 || address == ADDR_02)
            {
                display_data(data);
            }
        }
    }
}

以上程序仅供参考，具体实现过程中需要根据具体的单片机和通信协议进行调整。