modbus c语言源码

以下是一个简单的使用C语言实现Modbus协议的源代码示例，供参考：

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

#define SLAVE_ADDRESS 0x01

/* Modbus function codes */
#define READ_COILS 0x01
#define READ_DISCRETE_INPUTS 0x02
#define READ_HOLDING_REGISTERS 0x03
#define READ_INPUT_REGISTERS 0x04
#define WRITE_SINGLE_COIL 0x05
#define WRITE_SINGLE_REGISTER 0x06
#define WRITE_MULTIPLE_COILS 0x0F
#define WRITE_MULTIPLE_REGISTERS 0x10

/* Modbus exception codes */
#define EXCEPTION_ILLEGAL_FUNCTION 0x01
#define EXCEPTION_ILLEGAL_DATA_ADDRESS 0x02
#define EXCEPTION_ILLEGAL_DATA_VALUE 0x03
#define EXCEPTION_SLAVE_DEVICE_FAILURE 0x04
#define EXCEPTION_ACKNOWLEDGE 0x05
#define EXCEPTION_SLAVE_DEVICE_BUSY 0x06
#define EXCEPTION_MEMORY_PARITY_ERROR 0x08
#define EXCEPTION_GATEWAY_PATH_UNAVAILABLE 0x0A
#define EXCEPTION_GATEWAY_TARGET_DEVICE_FAILED_TO_RESPOND 0x0B

/* Modbus TCP/IP frame format */
typedef struct {
    uint16_t transaction_identifier;
    uint16_t protocol_identifier;
    uint16_t length;
    uint8_t unit_identifier;
    uint8_t function_code;
    uint8_t data[];
} modbus_frame_t;

/* Modbus response frame format */
typedef struct {
    uint16_t transaction_identifier;
    uint16_t protocol_identifier;
    uint16_t length;
    uint8_t unit_identifier;
    uint8_t function_code;
    uint8_t byte_count;
    uint8_t data[];
} modbus_response_t;

/* Modbus exception response frame format */
typedef struct {
    uint16_t transaction_identifier;
    uint16_t protocol_identifier;
    uint16_t length;
    uint8_t unit_identifier;
    uint8_t function_code;
    uint8_t exception_code;
} modbus_exception_t;

/* Calculate Modbus CRC */
uint16_t modbus_crc(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;
}

/* Send Modbus request and receive response */
int modbus_request(uint8_t *request, uint16_t request_length, uint8_t *response, uint16_t *response_length) {
    /* TODO: Implement Modbus request and response handling */
    return 0;
}

/* Read multiple holding registers */
int modbus_read_holding_registers(uint16_t register_address, uint16_t register_count, uint16_t *register_values) {
    uint8_t request[256];
    uint16_t request_length;
    uint8_t response[256];
    uint16_t response_length;

    /* Build Modbus request */
    request_length = 0;
    request[request_length++] = SLAVE_ADDRESS;
    request[request_length++] = READ_HOLDING_REGISTERS;
    request[request_length++] = (register_address >> 8) & 0xFF;
    request[request_length++] = register_address & 0xFF;
    request[request_length++] = (register_count >> 8) & 0xFF;
    request[request_length++] = register_count & 0xFF;

    /* Calculate Modbus CRC */
    uint16_t crc = modbus_crc(request, request_length);
    request[request_length++] = crc & 0xFF;
    request[request_length++] = (crc >> 8) & 0xFF;

    /* Send Modbus request and receive response */
    if (modbus_request(request, request_length, response, &response_length) != 0) {
        printf("Error: Modbus request failed!\n");
        return -1;
    }

    /* Parse Modbus response */
    modbus_response_t *modbus_response = (modbus_response_t *) response;
    if (modbus_response->unit_identifier != SLAVE_ADDRESS) {
        printf("Error: Invalid Modbus slave address!\n");
        return -1;
    }
    if (modbus_response->function_code == READ_HOLDING_REGISTERS + 0x80) {
        modbus_exception_t *modbus_exception = (modbus_exception_t *) response;
        printf("Error: Modbus exception code %d!\n", modbus_exception->exception_code);
        return -1;
    }
    if (modbus_response->function_code != READ_HOLDING_REGISTERS) {
        printf("Error: Invalid Modbus function code!\n");
        return -1;
    }
    if (modbus_response->byte_count != register_count * 2) {
        printf("Error: Invalid Modbus byte count!\n");
        return -1;
    }
    memcpy(register_values, modbus_response->data, register_count * 2);

    return 0;
}

/* Main function */
int main(int argc, char **argv) {
    /* Read holding registers */
    uint16_t register_values[16];
    if (modbus_read_holding_registers(0x0000, 16, register_values) != 0) {
        printf("Error: Failed to read Modbus holding registers!\n");
        return -1;
    }
    for (int i = 0; i < 16; i++) {
        printf("Register %d: %d\n", i, register_values[i]);
    }

    return 0;
}

请注意，这个示例仅仅是一个简单的模板，实际应用中需要根据具体情况进行修改和完善。同时，还需要实现Modbus协议的物理层和传输层，例如串口通信或TCP/IP通信。