实现上位机发送指令下位机回复指令

采用c8051f340单片机，用r485实现
指令随意

下位机 接收/回复

#include <c8051f340.h>
#define uchar unsigned char
#define uint unsigned int
/***********端口初始化函数+******************/
sbit Contrl = P0 ^ 1; //p0.1
char txt[100];
uint l = 0;
uint count = 0;
uint ll = 0;
char tmp;

void PORT_Init(void) {
    XBR0 = 0x01;//端口I/O交叉开关寄存器0
    XBR1 = 0x40;//端口I/O交叉开关寄存器1,交叉开关使能
    P0MDOUT = 0x10;//P0.4为推挽输出，其他的为漏极开路输出
    P0MDOUT |= 0x02;//P0.1也为推挽输出
}
void UART0_Init(void) {
    SCON0 |= 0x10;
    CKCON = 0x01;
    TH1 = 0x64;//波特率为9600
    TL1 = TH1;
    TMOD = 0x20;
    TR1 = 1;//P235，定时器1运行控制，定时器1允许
    TI0 = 1;//P235，中断1类型选择，INT1为边沿触发
}
void main() {
    char g;
    PCA0MD &= ~0x40;//关闭看门狗
    OSCICN |= 0x03;//P126
    PORT_Init();//端口初始化
    UART0_Init();//UART0初始化
    Contrl = 0;//485接收状态
    TI0 = 0;
    while (1) {
        if (l>0)
        {
            count++;
            if (count>1000)
            {

                Contrl = 1;//485发送状态
                ll = 0;
                while (ll < l)
                {
                    tmp= txt[ll]；
                    SBUF0 = tmp;
                    while (TI0 == 0);//发送
                    TI0 = 0;
                    ll++;
                }
                l = 0;
                Contrl = 0;//485接收状态
            }
        }


        if (RI0==0)
        {
            continue;
        }
        tmp= SBUF0；
        txt[l]= tmp;
        l++;
        RI0 = 0;
        count = 0;




    }
}

请各位帮忙