Used pins

For RS-485 communication protocol the defined Arduino Mega pins are showed in the chart below:

Then don’t forget to implement the proper initialization of your communication on the setup() function

NOTE: Check the velocity of transmition between the PLC and the Laptop and from the PLC to the device connected by RS-485.

RS-485 Library - Functions

* Remember that all the devices have to communicate at the same baudrate.

RS485.begin(baud); //sets the baud rate for RS485 data transmision
RS485.read(); //reads incoming RS485 data
RS485.write(byteToSend); //write binary data to RS485 port
RS485.write(dataToSend, dataLength); //write binary data to RS485 port
RS485.available() //returns the number of bytes available for reading on RS485 port

 This is all it’s necessary to know to use RS-485 on Industrial Shields equipments. Finally it is showed an example using RS-485.

Example Codes

Basic RS-485 write example (send):

// Include Industrial Shields libraries
#include <RS485.h>

//// IMPORTANT: check switches configuration

////////////////////////////////////////////////////////////////////////////////////////////////////
void setup() {
  // Begin serial port
	Serial.begin(9600);

  // Begin RS485 port
  RS485.begin(38400);
}

////////////////////////////////////////////////////////////////////////////////////////////////////
void loop() {
  // Wait bytes in the serial port
  if (Serial.available()) {
    byte tx = Serial.read();

    // Echo the byte to the serial port again
    Serial.write(tx);

    // And send it to the RS-485 port
    RS485.write(tx);
  }
}

Basic RS-485 read example (receive):

// Include Industrial Shields libraries
#include <RS485.h>

//// IMPORTANT: check switches configuration

////////////////////////////////////////////////////////////////////////////////////////////////////
void setup() {
  // Begin serial port
	Serial.begin(9600);

  // Begin RS485 port
  RS485.begin(38400);
}

////////////////////////////////////////////////////////////////////////////////////////////////////
void loop() {
  // Print received byte when available
  if (RS485.available()) {
    byte rx = RS485.read();

    // Hexadecimal representation
    Serial.print("HEX: ");
    Serial.print(rx, HEX);

    // Decimal representation
    Serial.print(", DEC: ");
    Serial.println(rx, DEC);
  }
}

* Remember that to do the full duplex test you must connect the A, B (receivers) to the Y, X(transmitters).