CH348结合开源ModBus协议组成串口温度采集服务器

前言

开源项目libmodbus

libmodbus作为免费的开发库，遵循标准Modbus协议的设备发送/接收数据。支持ModBus RTU、Modbus TCP。纯C代码编写，只有7个文件，体积小而稳定。
项目地址：
https://github.com/stephane/libmodbus

CH348 USB串口芯片

CH348是一款高速USB总线的转接芯片，实现USB转8个异步串口，每个串口最高波特率为6Mbps，支持CTS和RTS硬件自动流控，满足工业使用环境。
实际中可以利用USB HUB控制器芯片CH334，结合CH348，组成USB转32串口方案。
芯片详情：
CH348详情

方案详情

本次利用CH348硬件去读取八个从机的温度传感器数据，这里首要条件是保证从机与主机的串口通讯正常。这里分享下上位机的代码，介绍一下libmodbus的使用：

#include <iostream>
#include <string>
#include <vector>
#include "modbus.h"
using namespace std;
#define COMNUM 8
// 这里CH348是COM70到COM77
#define CONNUMSTART 70 

int main()
{
    vector<string> comname(COMNUM);
    vector<modbus_t*> mbArr(COMNUM);
    // 用于存储接受到的温度数据
    uint16_t table[3];
    // Modbus RTU初始化
    for (size_t i = 0; i < COMNUM; i++) {
        comname[i] = string("\\\\.\\") + string("COM") + to_string(CONNUMSTART + i);
        mbArr[i] = modbus_new_rtu(comname[i].c_str(), 115200, 'N', 8, 1);
        // 如需使用modbus tcp，此处应为改为类似modbus_new_tcp("slave IP ADDRESS", port_number);
        if (mbArr[i] == NULL) {
            modbus_free(mbArr[i]);
            printf("new rtu failed: %s\n", modbus_strerror(errno));
            return 0;
        }
        // i+1为设备地址，这里为设备1~设备8
        modbus_set_slave(mbArr[i], i + 1);
        if (modbus_connect(mbArr[i]) == -1) {
            modbus_close(mbArr[i]);
            modbus_free(mbArr[i]);
            printf("connect failed: %s\n", modbus_strerror(errno));
            return 0;
        }
    }
    std::cout << "Modbus master running...\n";
    int ret;
    while (1) {
        for (size_t i = 0; i < mbArr.size(); i++) {
        	// 从从机的0、1寄存器读取数据
            ret = modbus_read_registers(mbArr[i], 0, 2, table);
            if (ret == 2) {
                cout << "receive slave No." << i + 1 << " temperature : " << table[0] + (table[1] / 10.0f) << endl;
            } else {
                goto EXIT;
            }
            Sleep(50);
        }
        cout << "-------------------------------------------" << endl;
        // 每隔5秒轮询查询一遍温度数据
        Sleep(5000);
    }
EXIT:
    for (auto& p : mbArr) {
        modbus_close(p);
        modbus_free(p);
    }
}

首先运行从机，开始采集数据存储到0、1寄存器中，运行结果如下：

\Release>ModbusMaster.exe
Modbus master running!
receive slave No.1 temperature : 31.6
receive slave No.2 temperature : 30.3
receive slave No.3 temperature : 32.7
receive slave No.4 temperature : 31.7
receive slave No.5 temperature : 33.4
receive slave No.6 temperature : 30.7
receive slave No.7 temperature : 33.4
receive slave No.8 temperature : 33
-------------------------------------------
receive slave No.1 temperature : 32.9
receive slave No.2 temperature : 33.8
receive slave No.3 temperature : 32.3
receive slave No.4 temperature : 31.1
receive slave No.5 temperature : 32.7
receive slave No.6 temperature : 30.2
receive slave No.7 temperature : 30.6
receive slave No.8 temperature : 31.4
-------------------------------------------
receive slave No.1 temperature : 33.5
receive slave No.2 temperature : 33
receive slave No.3 temperature : 30
receive slave No.4 temperature : 30.9
receive slave No.5 temperature : 30
receive slave No.6 temperature : 33.2
receive slave No.7 temperature : 33.9
receive slave No.8 temperature : 32.1
-------------------------------------------