生成一段使用c语言的Modbus通讯协议实例代码

以下是一个使用c语言的Modbus通讯协议实例代码：

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

#define MODBUS_READ_COILS 0x01
#define MODBUS_READ_DISCRETE_INPUTS 0x02
#define MODBUS_READ_HOLDING_REGISTERS 0x03
#define MODBUS_READ_INPUT_REGISTERS 0x04
#define MODBUS_WRITE_SINGLE_COIL 0x05
#define MODBUS_WRITE_SINGLE_REGISTER 0x06
#define MODBUS_WRITE_MULTIPLE_COILS 0x0F
#define MODBUS_WRITE_MULTIPLE_REGISTERS 0x10

#define MODBUS_SLAVE_ADDRESS 0x01
#define MODBUS_FUNCTION_CODE MODBUS_READ_HOLDING_REGISTERS
#define MODBUS_START_ADDRESS 0x0000
#define MODBUS_REGISTER_COUNT 0x0002

int main(int argc, char *argv[]) {
    // Create Modbus request buffer
    uint8_t request[8];
    memset(request, 0, sizeof(request));

    // Set Modbus request values
    request[0] = MODBUS_SLAVE_ADDRESS;
    request[1] = MODBUS_FUNCTION_CODE;
    request[2] = (MODBUS_START_ADDRESS >> 8) & 0xFF;
    request[3] = MODBUS_START_ADDRESS & 0xFF;
    request[4] = (MODBUS_REGISTER_COUNT >> 8) & 0xFF;
    request[5] = MODBUS_REGISTER_COUNT & 0xFF;

    // Calculate Modbus CRC
    uint16_t crc = 0xFFFF;
    for (int i = 0; i < 6; i++) {
        crc ^= (uint16_t)request[i];
        for (int j = 0; j < 8; j++) {
            if (crc & 0x0001) {
                crc >>= 1;
                crc ^= 0xA001;
            } else {
                crc >>= 1;
            }
        }
    }
    request[6] = crc & 0xFF;
    request[7] = (crc >> 8) & 0xFF;

    // Send Modbus request over serial or TCP/IP
    // ...

    // Receive Modbus response over serial or TCP/IP
    // ...

    // Check Modbus response
    if (response[0] != MODBUS_SLAVE_ADDRESS) {
        printf("Error: Invalid Modbus slave address\n");
        return -1;
    }
    if (response[1] != MODBUS_FUNCTION_CODE) {
        printf("Error: Invalid Modbus function code\n");
        return -1;
    }
    if (response[2] != (MODBUS_REGISTER_COUNT * 2)) {
        printf("Error: Invalid Modbus register count\n");
        return -1;
    }

    // Parse Modbus response
    uint16_t *registers = malloc(MODBUS_REGISTER_COUNT * sizeof(uint16_t));
    for (int i = 0; i < MODBUS_REGISTER_COUNT; i++) {
        registers[i] = (response[3 + i * 2] << 8) | response[4 + i * 2];
    }

    // Print Modbus response
    printf("Modbus response:\n");
    for (int i = 0; i < MODBUS_REGISTER_COUNT; i++) {
        printf("Register %04X: %04X\n", MODBUS_START_ADDRESS + i, registers[i]);
    }

    // Free memory
    free(registers);

    return 0;
}

该代码实现了一个简单的Modbus读取保持寄存器的请求，并解析了响应。可以根据需要修改请求和响应的值以执行不同的Modbus操作。