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RS485 Component Documentation for the RS485 component that provides Modbus RTU communication over RS-485 serial protocol
RS485
Modbus
RTU
serial
industrial communication
ESP32

RS485

Path: src/RS485.cpp

Revision History: Initial documentation

The RS485 component provides Modbus RTU master functionality for industrial communications over the RS-485 serial protocol. It enables communication with various industrial devices that support the Modbus RTU protocol and acts as an interface between these devices and the internal system components.

REQUIREMENTS

Hardware

  • RS-485 transceiver (typically integrated on ESP32 industrial boards)
  • Properly wired RS-485 network (A/B/GND connections)

Software

  • ModbusClientRTU library for Modbus RTU communication
  • ModbusRTU and ModbusTypes dependencies
  • Configuration settings in config-modbus.h

FEATURES

  • Modbus RTU master implementation
  • Integration with Modbus TCP for remote access to RTU devices
  • Device management for multiple slave devices
  • Register read/write operations
  • Register change notifications
  • Periodic device polling

DEPENDENCIES

graph TD
    RS485 --> Component
    RS485 --> ModbusRTU
    RS485 --> ModbusTCP
    RS485 --> ModbusBlockView
    RS485 --> Manager

BEHAVIOUR

The RS485 component initializes during setup and then periodically polls connected devices in its loop function. It also handles Modbus TCP requests by translating them to RTU operations and manages the communication with the RTU slave devices.

stateDiagram-v2
    [*] --> Initialization
    Initialization --> Ready
    Ready --> ProcessingTcpRequests: TCP Request Received
    Ready --> PollingDevices: Timer Triggered
    ProcessingTcpRequests --> Ready: Response Sent
    PollingDevices --> Ready: Polling Complete
    Ready --> HandleRegisterChange: Register Changed
    HandleRegisterChange --> Ready

TODOS

PERFORMANCE

  • Optimize polling frequency based on device response times
  • Implement more efficient register caching to reduce network traffic
  • Consider batch operations for multiple registers to improve throughput

SECURITY

  • Implement proper error handling for malformed Modbus packets
  • Consider adding CRC validation for extra reliability
  • Implement timeout handling for unresponsive devices

COMPLIANCE

  • Ensure compliance with Modbus RTU specification
  • Validate against industrial standards for RS-485 communication
  • Test with different vendor implementations for compatibility

RECOMMENDATIONS

  • Use proper RS-485 termination resistors on the physical network
  • Configure appropriate timeouts based on network complexity and device count
  • Implement error recovery mechanisms for robust operation
  • Use shielded twisted pair cables for RS-485 connections in noisy environments

EXAMPLE

Below is an example of how the RS485 component might be constructed and mounted in an application:

#ifdef ENABLE_RS485
  rs485 = new RS485(
      this  // owner
  );
  if (rs485)
  {
    components.push_back(rs485);
    Log.infoln(F("RS485 initialized."));
  }
  else
  {
    Log.errorln(F("RS485 initialization failed."));
  }
#endif

References