Modbus485 Component

Modbus485

Path: src/modbus485.h

Revision History:

Initial documentation

A robust Modbus RTU communication component supporting RS-485 electrical interface for ESP-32 devices. This implementation features comprehensive error handling, logging, and state management, making it suitable for industrial applications requiring reliable communication.

REQUIREMENTS

Hardware:
- RS-485 transceiver (e.g., MAX485)
- UART TX pin
- UART RX pin
- DE/RE pin for direction control
Software:
- HardwareSerial
- ArduinoLog or similar for logging

FEATURES

Full Modbus RTU master client implementation
Configurable baud rate, parity, and stop bits
Support for multiple read and write function codes
Automatic transaction ID management
Comprehensive error handling and reporting
Response timeout management
Debug logging
Modbus frame validation (CRC16)
State machine design for reliable operation
Supports single and block operations for coils, discrete inputs, holding registers and input registers

DEPENDENCIES

BEHAVIOUR

TODOS

PERFORMANCE

Consider implementing a response parser to handle partial responses
Add transaction queuing to handle multiple concurrent requests
Optimize memory usage for constrained devices
Add retry mechanism for failed requests

SECURITY

Implement message authentication for critical operations
Consider encryption for sensitive data transmission
Add access control mechanisms for write operations
Implement session timeouts for maintaining connection state

COMPLIANCE

Ensure full compliance with Modbus RTU specification
Validate against Modbus conformance test suite
Document compatibility with specific Modbus devices

RECOMMENDATIONS

Use proper shielded cables for RS-485 communication
Implement proper termination resistors on the RS-485 bus
Consider using optically isolated RS-485 transceivers in noisy environments
Monitor response times and adjust timeouts accordingly
Implement application-level heartbeats for critical connections

EXAMPLE

#ifdef PIN_RS485_DE
  modbus485 = new Modbus485(
      this,            // owner
      PIN_RS485_TX,    // TX pin
      PIN_RS485_RX,    // RX pin
      PIN_RS485_DE,    // DE/RE pin
      RS485_BAUDRATE,  // baud rate
      RS485_CONFIG     // UART configuration
  );

  if (modbus485) {
    components.push_back(modbus485);
    Log.infoln(F("Modbus485 initialized. TX:%d, RX:%d, DE:%d, Baud:%d"),
               PIN_RS485_TX, PIN_RS485_RX, PIN_RS485_DE, RS485_BAUDRATE);
  } else {
    Log.errorln(F("Modbus485 initialization failed."));
  }
#endif