stc89c52 实现modbus从站

STC89C52芯片可以通过编程实现Modbus从站功能。下面是一个基本的Modbus从站实现代码示例：

#include <reg52.h>

#define DATA_LEN 8

unsigned char code ID = 0x01;
unsigned char xdata buf[DATA_LEN];
unsigned char xdata recv_buf[DATA_LEN];

void uart_init()
{
    TMOD = 0x20;
    SCON = 0x50;
    TH1 = 0xFD;
    TL1 = TH1;
    TR1 = 1;
}

void uart_send_data(unsigned char *data, unsigned char len)
{
    unsigned char i;

    for (i = 0; i < len; i++)
    {
        SBUF = data[i];
        while (!TI);
        TI = 0;
    }
}

void uart_recv_data(unsigned char *data, unsigned char len)
{
    unsigned char i;

    for (i = 0; i < len; i++)
    {
        while (!RI);
        data[i] = SBUF;
        RI = 0;
    }
}

unsigned short crc16(unsigned char *data, unsigned char len)
{
    unsigned short crc = 0xFFFF;
    unsigned char i, j;

    for (i = 0; i < len; i++)
    {
        crc ^= data[i];

        for (j = 0; j < 8; j++)
        {
            if (crc & 0x0001)
            {
                crc >>= 1;
                crc ^= 0xA001;
            }
            else
            {
                crc >>= 1;
            }
        }
    }

    return crc;
}

void modbus_process()
{
    unsigned char recv_len, i;
    unsigned short crc;

    if (RI)
    {
        recv_len = SBUF;
        uart_recv_data(recv_buf, recv_len - 1);
        crc = crc16(recv_buf, recv_len - 1);

        if ((recv_buf[0] == ID) && (crc == ((recv_buf[recv_len - 1] << 8) | recv_buf[recv_len - 2])))
        {
            switch (recv_buf[1])
            {
                case 0x03:
                    for (i = 0; i < DATA_LEN; i++)
                    {
                        buf[i] = i;
                    }

                    uart_send_data(&ID, 1);
                    uart_send_data("\x03", 1);
                    uart_send_data(buf, DATA_LEN);
                    crc = crc16(buf, DATA_LEN);
                    uart_send_data((unsigned char *)&crc, 2);
                    break;
                default:
                    break;
            }
        }
    }
}

void main()
{
    uart_init();

    while (1)
    {
        modbus_process();
    }
}

这是一个简单的Modbus从站实现代码，使用了STC89C52芯片的UART模块和CRC16校验。其中，ID为从站地址，buf为从站存储的数据。在modbus_process函数中，接收到数据后进行校验，如果校验正确并且命令是0x03（读保持寄存器），则将buf中的数据发送回主站。你可以根据实际需求进行修改和完善。