用C语言写出51单片机串口收发字符串的程序

可以的，以下是一个简单的示例程序：

#include <reg51.h>

#define FOSC 11059200L
#define BAUD 9600
#define DIVIDER (FOSC / 12 / BAUD)

void init_uart() {
    SCON = 0x50; // 8-bit data, 1 stop bit, receive enable
    TMOD &= 0x0F; // clear timer1 mode bits
    TMOD |= 0x20; // timer1 mode 2: 8-bit auto-reload
    TH1 = TL1 = 0 - DIVIDER; // set timer1 reload value
    TR1 = 1; // start timer1
    ES = 1; // enable serial interrupt
    EA = 1; // enable global interrupt
}

void send_char(char c) {
    SBUF = c;
    while (!TI);
    TI = 0;
}

void send_string(char *s) {
    while (*s) {
        send_char(*s++);
    }
}

char receive_char() {
    while (!RI);
    RI = 0;
    return SBUF;
}

void receive_string(char *buf, int len) {
    int i;
    for (i = 0; i < len - 1; i++) {
        buf[i] = receive_char();
        if (buf[i] == '\r' || buf[i] == '\n') {
            break;
        }
    }
    buf[i] = '\0';
}

void main() {
    char buf[64];
    init_uart();
    while (1) {
        receive_string(buf, sizeof(buf));
        send_string("You said: ");
        send_string(buf);
        send_string("\r\n");
    }
}

void serial_isr() interrupt 4 {
    // do nothing
}