一、原理及工具

Modbus Slaves软件的使用：传送门

Modbus 协议原理：传送门

Modbus poll 和 Modbus slave调试工具下载：传送门

二、实验流程及相关源码

(1)设置ip和端口号

打开Modbus slave进行相关设置(注意这里IP和端口号可以自己进行相应设置)，具体如下：

(2)设置从站id

初始显示地址(Address)和显示行数(Quantity)及表格行数(Rows)

(3)查看报文

在Display-》Communication中可以看到发送(Tx)和接收(Rx)的报文

(4)源码及测试

Modbus从站读写寄存器相关API函数如下,注意下面的代码只能读正数不能读负数，若想读负数请自行脑补或到文末下载代码：

/* modbus.h*/#ifndef MODBUSPP_MODBUS_H
#define MODBUSPP_MODBUS_H#include <cstring>
#include <stdint.h>
#include <string>#ifdef ENABLE_MODBUSPP_LOGGING
#include <cstdio>
#define LOG(fmt, ...) printf("[ modbuspp ]" fmt, ##__VA_ARGS__)
#else
#define LOG(...) (void)0
#endif#ifdef _WIN32
// WINDOWS socket
#define _WINSOCK_DEPRECATED_NO_WARNINGS#include <winsock2.h>
#pragma comment(lib, "Ws2_32.lib")
using X_SOCKET = SOCKET;
using ssize_t = int;#define X_ISVALIDSOCKET(s) ((s) != INVALID_SOCKET)
#define X_CLOSE_SOCKET(s) closesocket(s)
#define X_ISCONNECTSUCCEED(s) ((s) != SOCKET_ERROR)#else
// Berkeley socket
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
using X_SOCKET = int;#define X_ISVALIDSOCKET(s) ((s) >= 0)
#define X_CLOSE_SOCKET(s) close(s)
#define X_ISCONNECTSUCCEED(s) ((s) >= 0)
#endifusing SOCKADDR = struct sockaddr;
using SOCKADDR_IN = struct sockaddr_in;#define MAX_MSG_LENGTH 260///Function Code
#define READ_COILS 0x01
#define READ_INPUT_BITS 0x02
#define READ_REGS 0x03
#define READ_INPUT_REGS 0x04
#define WRITE_COIL 0x05
#define WRITE_REG 0x06
#define WRITE_COILS 0x0F
#define WRITE_REGS 0x10///Exception Codes#define EX_ILLEGAL_FUNCTION 0x01 // Function Code not Supported
#define EX_ILLEGAL_ADDRESS 0x02  // Output Address not exists
#define EX_ILLEGAL_VALUE 0x03    // Output Value not in Range
#define EX_SERVER_FAILURE 0x04   // Slave Deive Fails to process request
#define EX_ACKNOWLEDGE 0x05      // Service Need Long Time to Execute
#define EX_SERVER_BUSY 0x06      // Server Was Unable to Accept MB Request PDU
#define EX_NEGATIVE_ACK 0x07
#define EX_MEM_PARITY_PROB 0x08
#define EX_GATEWAY_PROBLEMP 0x0A // Gateway Path not Available
#define EX_GATEWYA_PROBLEMF 0x0B // Target Device Failed to Response
#define EX_BAD_DATA 0XFF         // Bad Data lenght or Address#define BAD_CON -1/// Modbus Operator Class
/*** Modbus Operator Class* Providing networking support and mobus operation support.*/
class modbus
{public:bool err{};int err_no{};std::string error_msg;modbus(std::string host, uint16_t port);~modbus();bool modbus_connect();void modbus_close() const;void modbus_set_slave_id(int id);int modbus_read_coils(uint16_t address, uint16_t amount, bool *buffer);int modbus_read_input_bits(uint16_t address, uint16_t amount, bool *buffer);int modbus_read_holding_registers(uint16_t address, uint16_t amount, uint16_t *buffer);int modbus_read_input_registers(uint16_t address, uint16_t amount, uint16_t *buffer);int modbus_write_coil(uint16_t address, const bool &to_write);int modbus_write_register(uint16_t address, const uint16_t &value);int modbus_write_coils(uint16_t address, uint16_t amount, const bool *value);int modbus_write_registers(uint16_t address, uint16_t amount, const uint16_t *value);private:bool _connected{};uint16_t PORT{};uint32_t _msg_id{};int _slaveid{};std::string HOST;X_SOCKET _socket{};SOCKADDR_IN _server{};#ifdef _WIN32WSADATA wsadata;
#endifinline void modbus_build_request(uint8_t *to_send, uint16_t address, int func) const;int modbus_read(uint16_t address, uint16_t amount, int func);int modbus_write(uint16_t address, uint16_t amount, int func, const uint16_t *value);inline ssize_t modbus_send(uint8_t *to_send, size_t length);inline ssize_t modbus_receive(uint8_t *buffer) const;void modbuserror_handle(const uint8_t *msg, int func);inline void set_bad_con();inline void set_bad_input();
};/*** Main Constructor of Modbus Connector Object* @param host IP Address of Host* @param port Port for the TCP Connection* @return     A Modbus Connector Object*/
modbus::modbus(std::string host, uint16_t port = 502)
{HOST = host;PORT = port;_slaveid = 1;_msg_id = 1;_connected = false;err = false;err_no = 0;error_msg = "";
}/*** Destructor of Modbus Connector Object*/
modbus::~modbus(void) = default;/*** Modbus Slave ID Setter* @param id  ID of the Modbus Server Slave*/
void modbus::modbus_set_slave_id(int id)
{_slaveid = id;
}/*** Build up a Modbus/TCP Connection* @return   If A Connection Is Successfully Built*/
bool modbus::modbus_connect()
{if (HOST.empty() || PORT == 0){LOG("Missing Host and Port");return false;}else{LOG("Found Proper Host %s and Port %d", HOST.c_str(), PORT);}#ifdef _WIN32if (WSAStartup(0x0202, &wsadata)){return false;}
#endif_socket = socket(AF_INET, SOCK_STREAM, 0);if (!X_ISVALIDSOCKET(_socket)){LOG("Error Opening Socket");
#ifdef _WIN32WSACleanup();
#endifreturn false;}else{LOG("Socket Opened Successfully");}#ifdef WIN32const DWORD timeout = 20;
#elsestruct timeval timeout{};timeout.tv_sec = 20; // after 20 seconds connect() will timeouttimeout.tv_usec = 0;
#endifsetsockopt(_socket, SOL_SOCKET, SO_SNDTIMEO, (const char *)&timeout, sizeof(timeout));setsockopt(_socket, SOL_SOCKET, SO_RCVTIMEO, (const char *)&timeout, sizeof(timeout));_server.sin_family = AF_INET;_server.sin_addr.s_addr = inet_addr(HOST.c_str());_server.sin_port = htons(PORT);if (!X_ISCONNECTSUCCEED(connect(_socket, (SOCKADDR *)&_server, sizeof(_server)))){LOG("Connection Error");
#ifdef _WIN32WSACleanup();
#endifreturn false;}LOG("Connected");_connected = true;return true;
}/*** Close the Modbus/TCP Connection*/
void modbus::modbus_close() const
{X_CLOSE_SOCKET(_socket);
#ifdef _WIN32WSACleanup();
#endifLOG("Socket Closed");
}/*** Modbus Request Builder* @param to_send   Message Buffer to Be Sent* @param address   Reference Address* @param func      Modbus Functional Code*/
void modbus::modbus_build_request(uint8_t *to_send, uint16_t address, int func) const
{to_send[0] = (uint8_t)(_msg_id >> 8u);to_send[1] = (uint8_t)(_msg_id & 0x00FFu);to_send[2] = 0;to_send[3] = 0;to_send[4] = 0;to_send[6] = (uint8_t)_slaveid;to_send[7] = (uint8_t)func;to_send[8] = (uint8_t)(address >> 8u);to_send[9] = (uint8_t)(address & 0x00FFu);
}/*** Write Request Builder and Sender* @param address   Reference Address* @param amount    Amount of data to be Written* @param func      Modbus Functional Code* @param value     Data to Be Written*/
int modbus::modbus_write(uint16_t address, uint16_t amount, int func, const uint16_t *value)
{int status = 0;uint8_t *to_send;if (func == WRITE_COIL || func == WRITE_REG){to_send = new uint8_t[12];modbus_build_request(to_send, address, func);to_send[5] = 6;to_send[10] = (uint8_t)(value[0] >> 8u);to_send[11] = (uint8_t)(value[0] & 0x00FFu);status = modbus_send(to_send, 12);}else if (func == WRITE_REGS){to_send = new uint8_t[13 + 2 * amount];modbus_build_request(to_send, address, func);to_send[5] = (uint8_t)(7 + 2 * amount);to_send[10] = (uint8_t)(amount >> 8u);to_send[11] = (uint8_t)(amount & 0x00FFu);to_send[12] = (uint8_t)(2 * amount);for (int i = 0; i < amount; i++){to_send[13 + 2 * i] = (uint8_t)(value[i] >> 8u);to_send[14 + 2 * i] = (uint8_t)(value[i] & 0x00FFu);}status = modbus_send(to_send, 13 + 2 * amount);}else if (func == WRITE_COILS){to_send = new uint8_t[14 + (amount - 1) / 8];modbus_build_request(to_send, address, func);to_send[5] = (uint8_t)(7 + (amount + 7) / 8);to_send[10] = (uint8_t)(amount >> 8u);to_send[11] = (uint8_t)(amount & 0x00FFu);to_send[12] = (uint8_t)((amount + 7) / 8);for (int i = 0; i < (amount + 7) / 8; i++)to_send[13 + i] = 0; // init needed before summing!for (int i = 0; i < amount; i++){to_send[13 + i / 8] += (uint8_t)(value[i] << (i % 8u));}status = modbus_send(to_send, 14 + (amount - 1) / 8);}delete[] to_send;return status;
}/*** Read Request Builder and Sender* @param address   Reference Address* @param amount    Amount of Data to Read* @param func      Modbus Functional Code*/
int modbus::modbus_read(uint16_t address, uint16_t amount, int func)
{uint8_t to_send[12];modbus_build_request(to_send, address, func);to_send[5] = 6;to_send[10] = (uint8_t)(amount >> 8u);to_send[11] = (uint8_t)(amount & 0x00FFu);return modbus_send(to_send, 12);
}/*** Read Holding Registers* MODBUS FUNCTION 0x03* @param address    Reference Address* @param amount     Amount of Registers to Read* @param buffer     Buffer to Store Data Read from Registers*/
int modbus::modbus_read_holding_registers(uint16_t address, uint16_t amount, uint16_t *buffer)
{if (_connected){modbus_read(address, amount, READ_REGS);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, READ_REGS);if (err)return err_no;for (auto i = 0; i < amount; i++){buffer[i] = ((uint16_t)to_rec[9u + 2u * i]) << 8u;buffer[i] += (uint16_t)to_rec[10u + 2u * i];}return 0;}else{set_bad_con();return BAD_CON;}
}/*** Read Input Registers* MODBUS FUNCTION 0x04* @param address     Reference Address* @param amount      Amount of Registers to Read* @param buffer      Buffer to Store Data Read from Registers*/
int modbus::modbus_read_input_registers(uint16_t address, uint16_t amount, uint16_t *buffer)
{if (_connected){modbus_read(address, amount, READ_INPUT_REGS);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, READ_INPUT_REGS);if (err)return err_no;for (auto i = 0; i < amount; i++){buffer[i] = ((uint16_t)to_rec[9u + 2u * i]) << 8u;buffer[i] += (uint16_t)to_rec[10u + 2u * i];}return 0;}else{set_bad_con();return BAD_CON;}
}/*** Read Coils* MODBUS FUNCTION 0x01* @param address     Reference Address* @param amount      Amount of Coils to Read* @param buffer      Buffer to Store Data Read from Coils*/
int modbus::modbus_read_coils(uint16_t address, uint16_t amount, bool *buffer)
{if (_connected){if (amount > 2040){set_bad_input();return EX_BAD_DATA;}modbus_read(address, amount, READ_COILS);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, READ_COILS);if (err)return err_no;for (auto i = 0; i < amount; i++){buffer[i] = (bool)((to_rec[9u + i / 8u] >> (i % 8u)) & 1u);}return 0;}else{set_bad_con();return BAD_CON;}
}/*** Read Input Bits(Discrete Data)* MODBUS FUNCITON 0x02* @param address   Reference Address* @param amount    Amount of Bits to Read* @param buffer    Buffer to store Data Read from Input Bits*/
int modbus::modbus_read_input_bits(uint16_t address, uint16_t amount, bool *buffer)
{if (_connected){if (amount > 2040){set_bad_input();return EX_BAD_DATA;}modbus_read(address, amount, READ_INPUT_BITS);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}if (err)return err_no;for (auto i = 0; i < amount; i++){buffer[i] = (bool)((to_rec[9u + i / 8u] >> (i % 8u)) & 1u);}modbuserror_handle(to_rec, READ_INPUT_BITS);return 0;}else{return BAD_CON;}
}/*** Write Single Coils* MODBUS FUNCTION 0x05* @param address    Reference Address* @param to_write   Value to be Written to Coil*/
int modbus::modbus_write_coil(uint16_t address, const bool &to_write)
{if (_connected){int value = to_write * 0xFF00;modbus_write(address, 1, WRITE_COIL, (uint16_t *)&value);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, WRITE_COIL);if (err)return err_no;return 0;}else{set_bad_con();return BAD_CON;}
}/*** Write Single Register* FUCTION 0x06* @param address   Reference Address* @param value     Value to Be Written to Register*/
int modbus::modbus_write_register(uint16_t address, const uint16_t &value)
{if (_connected){modbus_write(address, 1, WRITE_REG, &value);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, WRITE_COIL);if (err)return err_no;return 0;}else{set_bad_con();return BAD_CON;}
}/*** Write Multiple Coils* MODBUS FUNCTION 0x0F* @param address  Reference Address* @param amount   Amount of Coils to Write* @param value    Values to Be Written to Coils*/
int modbus::modbus_write_coils(uint16_t address, uint16_t amount, const bool *value)
{if (_connected){uint16_t *temp = new uint16_t[amount];for (int i = 0; i < amount; i++){temp[i] = (uint16_t)value[i];}modbus_write(address, amount, WRITE_COILS, temp);delete[] temp;uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, WRITE_COILS);if (err)return err_no;return 0;}else{set_bad_con();return BAD_CON;}
}/*** Write Multiple Registers* MODBUS FUNCION 0x10* @param address Reference Address* @param amount  Amount of Value to Write* @param value   Values to Be Written to the Registers*/
int modbus::modbus_write_registers(uint16_t address, uint16_t amount, const uint16_t *value)
{if (_connected){modbus_write(address, amount, WRITE_REGS, value);uint8_t to_rec[MAX_MSG_LENGTH];ssize_t k = modbus_receive(to_rec);if (k == -1){set_bad_con();return BAD_CON;}modbuserror_handle(to_rec, WRITE_REGS);if (err)return err_no;return 0;}else{set_bad_con();return BAD_CON;}
}/*** Data Sender* @param to_send Request to Be Sent to Server* @param length  Length of the Request* @return        Size of the request*/
ssize_t modbus::modbus_send(uint8_t *to_send, size_t length)
{_msg_id++;return send(_socket, (const char *)to_send, (size_t)length, 0);
}/*** Data Receiver* @param buffer Buffer to Store the Data Retrieved* @return       Size of Incoming Data*/
ssize_t modbus::modbus_receive(uint8_t *buffer) const
{return recv(_socket, (char *)buffer, 1024, 0);
}void modbus::set_bad_con()
{err = true;error_msg = "BAD CONNECTION";
}void modbus::set_bad_input()
{err = true;error_msg = "BAD FUNCTION INPUT";
}/*** Error Code Handler* @param msg   Message Received from the Server* @param func  Modbus Functional Code*/
void modbus::modbuserror_handle(const uint8_t *msg, int func)
{err = false;error_msg = "NO ERR";if (msg[7] == func + 0x80){err = true;switch (msg[8]){case EX_ILLEGAL_FUNCTION:error_msg = "1 Illegal Function";break;case EX_ILLEGAL_ADDRESS:error_msg = "2 Illegal Address";break;case EX_ILLEGAL_VALUE:error_msg = "3 Illegal Value";break;case EX_SERVER_FAILURE:error_msg = "4 Server Failure";break;case EX_ACKNOWLEDGE:error_msg = "5 Acknowledge";break;case EX_SERVER_BUSY:error_msg = "6 Server Busy";break;case EX_NEGATIVE_ACK:error_msg = "7 Negative Acknowledge";break;case EX_MEM_PARITY_PROB:error_msg = "8 Memory Parity Problem";break;case EX_GATEWAY_PROBLEMP:error_msg = "10 Gateway Path Unavailable";break;case EX_GATEWYA_PROBLEMF:error_msg = "11 Gateway Target Device Failed to Respond";break;default:error_msg = "UNK";break;}}
}#endif //MODBUSPP_MODBUS_H

测试代码如下：

/*test.cpp
*/
#include "modbus.h"int main(int argc, char **argv)
{// create a modbus objectmodbus mb = modbus("127.0.0.1", 502);// set slave idmb.modbus_set_slave_id(1);// connect with the servermb.modbus_connect();// read coil                        function 0x01bool read_coil;mb.modbus_read_coils(0, 1, &read_coil);// read input bits(discrete input)  function 0x02bool read_bits;mb.modbus_read_input_bits(0, 1, &read_bits);// read holding registers           function 0x03uint16_t read_holding_regs[1];mb.modbus_read_holding_registers(0, 1, read_holding_regs);// read input registers             function 0x04uint16_t read_input_regs[1];mb.modbus_read_input_registers(0, 1, read_input_regs);// write single coil                function 0x05mb.modbus_write_coil(0, true);// write single reg                 function 0x06mb.modbus_write_register(0, 123);// write multiple coils             function 0x0Fbool write_cols[4] = {true, true, true, true};mb.modbus_write_coils(0, 4, write_cols);// write multiple regs              function 0x10uint16_t write_regs[4] = {123, 123, 123};mb.modbus_write_registers(0, 4, write_regs);// close connection and free the memorymb.modbus_close();return 0;
}

三、效果

含有负数数据的读写：传送门

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