Industrial bus

Modbus

The language existing industrial hosts already speak. Serial or TCP.

Industrial bus Modbus ESP32 family

Official path: examples/protocols/modbus

01 Overview

Modbus is one of the most common industrial protocols, and ESP-IDF provides official master/slave examples (path may shift slightly by IDF version).

It solves heterogeneous device interconnection: PLCs, meters, and VFDs often only speak Modbus, and ESP32 can bridge them to Wi-Fi or the cloud.

Use it when integrating with existing industrial hosts, sensor acquisition, or remote monitoring.

Skip it for consumer app control; BLE or HTTP is more appropriate.

Modbus has two physical layers: RTU over serial (usually RS485) and TCP over Ethernet or Wi-Fi.

This page focuses on ESP32 as a slave or master implementation points.

02 Hardware

MCU: ESP32 family with built-in UART and Wi-Fi, suitable for both Modbus RTU and TCP.
RS485 transceiver: RTU mode requires an external RS485 chip (e.g., MAX485), connected to ESP32 UART TX/RX and a GPIO for direction control.
Termination resistors: 120Ω at both ends of the RS485 bus; see schematic.
Isolation: Industrial sites often require isolated RS485 modules to prevent ground loops.
TCP mode: Use ESP32 Wi-Fi to connect to the LAN; ensure the field VLAN is reachable.
Power: Check transceiver supply voltage (typically 3.3V or 5V); see schematic.
Wiring: Ensure A/B lines are correct; reversed polarity causes communication failure.

03 Software flow

1. Choose RTU or TCP mode; configure UART or Wi-Fi accordingly.

2. Set slave address (1-247) and baud rate (e.g., 9600/115200).

3. Define the register map: holding registers, input registers, coils, etc.

4. Map real sensor data to register addresses.

5. Implement master or slave callbacks to handle read/write requests.

6. Add error handling: CRC failures, timeouts, exception codes.

7. Test with a Modbus debugging tool to verify communication.

8. Consider low power: sleep when idle, wake periodically for polling.

04 Core points

The register map is the product spec. Agree it before coding.
Custom work: point list, RS485, cloud in parallel.
Baud rate and parity must match the host, or communication fails.
RS485 direction control needs precise timing, or data collisions occur.
Don't copy Modbus implementations from other chips; ESP32 UART and interrupt handling differ.
For TCP mode, manage connections carefully to avoid multiple hosts connecting simultaneously.

中文

工业总线

Modbus

进现有工业主机的常用语言。串口或 TCP。

工业总线 Modbus ESP32 family

官方路径: examples/protocols/modbus

01 项目概述

Modbus 是工业现场最常见的通信协议之一，ESP-IDF 官方提供主从示例，路径随 IDF 版本略有调整。

它解决的是异构设备互联问题：PLC、电表、变频器等设备往往只支持 Modbus，通过 ESP32 可以桥接到 Wi-Fi 或云。

适用于需要对接现有工业主机、传感器采集、远程监控等场景。

不适用于消费级 App 控制，那种场景用 BLE 或 HTTP 更合适。

Modbus 有两种物理层：RTU 走串口（通常 RS485），TCP 走以太网或 Wi-Fi。

本页聚焦 ESP32 作为从站或主站的实现要点。

02 项目硬件描述

MCU: ESP32 系列，内置 UART 和 Wi-Fi，适合 Modbus RTU 和 TCP。
RS485 收发器: RTU 模式需要外部 RS485 芯片（如 MAX485），连接 ESP32 的 UART TX/RX 和 GPIO 控制方向。
终端电阻: RS485 总线两端需 120Ω 终端电阻，具体见原理图。
隔离: 工业现场建议使用隔离型 RS485 模块，防止地环路损坏设备。
TCP 模式: 使用 ESP32 的 Wi-Fi 连接局域网，确保现场 VLAN 能通。
电源: 注意 RS485 收发器的供电电压（通常 3.3V 或 5V），见原理图。
接线: 确保 A/B 线正确，极性反了会导致通信失败。

03 项目软件流程描述

1. 选择 RTU 或 TCP 模式，配置 UART 或 Wi-Fi。

2. 配置从站地址（1-247）和波特率（如 9600/115200）。

3. 定义寄存器表：保持寄存器、输入寄存器、线圈等。

4. 将真实传感器数据映射到寄存器地址。

5. 实现主站或从站回调，处理读写请求。

6. 添加错误处理：CRC 校验失败、超时、异常码。

7. 测试：使用 Modbus 调试工具验证通信。

8. 考虑低功耗：在空闲时进入睡眠，定时唤醒轮询。

04 项目核心点

寄存器表就是产品说明书。 先和客户对表再写代码。
可定制： 点表、RS485、和云并行。
注意波特率和校验位 必须与主机一致，否则通信失败。
RS485 方向控制 需要精确时序，否则数据冲突。
不要照搬其他芯片的 Modbus 实现，ESP32 的 UART 和中断处理不同。
TCP 模式注意连接管理，避免多个主机同时连接。