用c写一段modbus协议

Modbus是一种通信协议，可用于连接不同的设备和系统，使它们之间可以相互通信和交换数据。以下是一个使用C语言编写的Modbus协议的示例：

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

#define MAX_BUFFER_SIZE 256

// Function to calculate Modbus CRC
uint16_t calculateCRC(uint8_t *data, uint16_t length) {
    uint16_t crc = 0xFFFF;
    uint8_t i, j;

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

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

    return crc;
}

// Function to create Modbus packet
void createModbusPacket(uint8_t *buffer, uint8_t slaveID, uint8_t functionCode, uint16_t startingAddress, uint16_t quantity) {
    uint16_t crc;
    uint8_t packetLength = 6;

    buffer[0] = slaveID;
    buffer[1] = functionCode;
    buffer[2] = (startingAddress >> 8) & 0xFF;
    buffer[3] = startingAddress & 0xFF;
    buffer[4] = (quantity >> 8) & 0xFF;
    buffer[5] = quantity & 0xFF;

    crc = calculateCRC(buffer, packetLength);
    buffer[packetLength++] = crc & 0xFF;
    buffer[packetLength++] = (crc >> 8) & 0xFF;
}

// Function to send Modbus packet
bool sendModbusPacket(uint8_t *buffer, uint16_t length) {
    // Code to send Modbus packet
    return true;
}

// Main function
int main() {
    uint8_t buffer[MAX_BUFFER_SIZE];
    uint8_t slaveID = 1;
    uint8_t functionCode = 3;
    uint16_t startingAddress = 0;
    uint16_t quantity = 10;

    createModbusPacket(buffer, slaveID, functionCode, startingAddress, quantity);
    sendModbusPacket(buffer, 8);

    return 0;
}

这个示例包括了一个计算Modbus CRC的函数、一个创建Modbus数据包的函数以及一个发送Modbus数据包的函数。在主函数中，我们创建了一个Modbus数据包并将其发送出去。根据实际情况，你可能需要调整一些参数和代码以适应你的应用场景。