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ModbusRTU - Industrial Modbus-485 RTU Interface

ModbusRTU

Section titled “ModbusRTU”

Path: src/modbus/ModbusRTU.h

Revision History: Initial documentation

ModbusRTU is a comprehensive class that provides a robust interface for Modbus RTU communication over RS-485. It is designed for industrial applications on ESP32, offering efficient queue management, adaptive timeouts, and extensive error handling capabilities.

REQUIREMENTS

Section titled “REQUIREMENTS”

  • Hardware:

    • ESP32 microcontroller
    • RS-485 transceiver (with DE/RE pin for direction control)
    • Serial interface for communication

  • Software:

    • Arduino framework
    • ModbusClientRTU library
    • HardwareSerial for serial communication
    • ArduinoLog for logging

PROVIDES

Section titled “PROVIDES”

  • Enumerations:

    • E_InitState: Tracks initialization states (INIT_NOT_STARTED, INIT_SERIAL_STARTED, INIT_CLIENT_STARTED, INIT_READY, INIT_FAILED)

  • Classes:

    • ModbusRTU: Main class for Modbus RTU communication
    • Manager: Device management class for handling multiple Modbus slave devices

FEATURES

Section titled “FEATURES”
  • Non-blocking initialization and operation
  • Flexible queue management with priority levels
  • Read/write operations for coils and registers (single and multiple)
  • Automatic value caching with synchronization status tracking
  • Comprehensive error handling and retry mechanisms
  • Adaptive minimum operation interval to adjust for network conditions
  • Filter chain for operation validation and duplicate prevention
  • Callback system for register changes, write completions, and error handling
  • Status reporting and debugging utilities

DEPENDENCIES

Section titled “DEPENDENCIES”

ModbusRTU

Arduino

ModbusClientRTU

HardwareSerial

ArduinoLog

ModbusTypes

Manager

BEHAVIOUR

Section titled “BEHAVIOUR”

begin()

Serial init delay elapsed

Client init delay elapsed

end()

Error

Error

Error

Ready for operations

INIT_NOT_STARTED

INIT_SERIAL_STARTED

INIT_CLIENT_STARTED

INIT_READY

INIT_FAILED

Operations

Read/Write request

Apply filters

If passed filters

If rejected

Operation sent

Response received

Timeout/Error

Update cache

If retries < max

If max retries exceeded

After backoff

Idle

QueueOperation

FilterOperation

ExecuteOperation

WaitForResponse

ProcessResponse

HandleError

Retry

TODOS

Section titled “TODOS”

PERFORMANCE

Section titled “PERFORMANCE”
  • Consider buffer pooling for multiple register operations to reduce memory fragmentation
  • Implement batch processing for adjacent registers to reduce number of transactions
  • Explore more granular timeouts for different device types or operation types

SECURITY

Section titled “SECURITY”
  • Implement authentication mechanisms for secure Modbus communication
  • Add validation for incoming data values to prevent exploitation
  • Consider adding packet encryption for sensitive industrial applications

COMPLIANCE

Section titled “COMPLIANCE”
  • Ensure full compliance with Modbus RTU protocol specification
  • Add support for additional function codes to cover all Modbus operations
  • Implement proper exception code handling according to the standard

RECOMMENDATIONS

Section titled “RECOMMENDATIONS”
  • Monitor operation success rates and adjust retry limits based on network reliability
  • Configure adaptive timeouts based on device response characteristics
  • Implement device-specific wrappers for common industrial equipment
  • Use high priority flag for critical operations (safety or timing-sensitive commands)