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README
LGPL-2.1

LIBMODBUS

不再维护

libmodbus 放弃维护,推荐使用轻量级 Modbus 协议栈 agile_modbus

1、介绍

libmodbus是一个与使用Modbus协议的设备进行数据发送/接收的库。该库包含各种后端通过不同网络进行通信(例如,RTU模式下的串口或TCP / IPv6中的以太网)。

libmodbus提供了较低通信层的抽象,并在所有支持的平台上提供相同的API。

本源码实现了在RT-Thread上的移植,支持MODBUS-RTU和MODBUS-TCP。源码地址: https://github.com/loogg/libmodbus 作者:loogg

1.1、使用背景

Modbus 协议是应用于电子控制器上的一种通用语言。通过此协议,控制器相互之间、控制器经由网络(例如以太网)和其它设备之间可以通信。它已经成为一通用工业标准。有了它,不同厂商生产的控制设备可以连成工业网络,进行集中监控。此协议定义了一个控制器能认识使用的消息结构,而不管它们是经过何种网络进行通信的。它描述了一控制器请求访问其它设备的过程,如何回应来自其它设备的请求,以及怎样侦测错误并记录。它制定了消息域格局和内容的公共格式。当在一Modbus网络上通信时,此协议决定了每个控制器须要知道它们的设备地址,识别按地址发来的消息,决定要产生何种行动。如果需要回应,控制器将生成反馈信息并用Modbus 协议发出。在其它网络上,包含了 Modbus 协议的消息转换为在此网络上使用的帧或包结构。这种转换也扩展了根据具体的网络解决节地址、路由路径及错误检测的方法。

1.2、目录结构

名称 说明
docs 文档目录
examples 例子目录,并有相应的一些说明
inc 头文件目录
src 源代码目录

1.3、许可证

libmodbus package 遵循 LGPLv2.1 许可,详见 LICENSE 文件。

1.4、依赖

  • RT-Thread 4.0+
  • Filesystem
  • libc
  • pin
  • serial
  • POSIX
  • SAL

2、如何打开 libmodbus

使用 libmodbus package 需要在 RT-Thread 的包管理器中选择它,具体路径如下:

RT-Thread online packages
    IoT - internet of things --->
        [*] libmodbus: A Modbus library for RT-Thread

然后让 RT-Thread 的包管理器自动更新,或者使用 pkgs --update 命令更新包到 BSP 中。

3、使用 libmodbus

在打开 libmodbus package 后,当进行 bsp 编译时,它会被加入到 bsp 工程中进行编译。

3.1、创建modbus RTU 环境

  • 初始化RTU环境指针
modbus_t *modbus_new_rtu(const char *device, int baud,char parity, int data_bit, int stop_bit)
  • 设置串口模式
int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode)
  • 在RTU环境下设置RTS模式,为RS485模式下设置控制引脚
int modbus_rtu_set_rts(modbus_t *ctx, int rts_pin, int mode)
mode 说明
MODBUS_RTU_RTS_NONE 无控制
MODBUS_RTU_RTS_UP 高电平为发送模式
MODBUS_RTU_RTS_DOWN 低电平为发送模式

3.2、创建modbus TCP 环境

  • 初始化TCP环境指针
modbus_t *modbus_new_tcp(const char *ip, int port)
  • 作为客户端连接服务器
int modbus_connect(modbus_t *ctx)
  • 作为服务器监听
int modbus_tcp_listen(modbus_t * ctx, int nb_connection)

int modbus_tcp_accept(modbus_t * ctx, int * s)

3.3、示例

MODBUS-RTU和MODBUS-TCP使用示例在 /examples 下,使用方法与原生libmodbus一致。

4、注意事项

在使用RTU-RS485模式时,先设置引脚模式,再设置RS485模式,再设置控制引脚

rt_pin_mode(MAX3491_RE, PIN_MODE_OUTPUT);
modbus_t *ctx = RT_NULL;
ctx = modbus_new_rtu("/dev/uart2", 115200, 'N', 8, 1);
modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
modbus_rtu_set_rts(ctx, MAX3491_RE, MODBUS_RTU_RTS_UP);

其余API和libmodbus官方一致

5、联系方式 & 感谢

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