#define SSerialTxControl 3   //RS485 Direction control

#define RS485Transmit    HIGH
#define RS485Receive     LOW

#define Pin13LED         13

/*-----( Declare objects )-----*/


/*-----( Declare Variables )-----*/
int byteReceived;
int byteSend;

void setup()   /****** SETUP: RUNS ONCE ******/
{
  // Start the built-in serial port, probably to Serial Monitor
  Serial.begin(19200);
  pinMode(Pin13LED, OUTPUT);   
  pinMode(SSerialTxControl, OUTPUT);    
  
  digitalWrite(SSerialTxControl, RS485Receive);  // Init Transceiver   
  
  // Start the software serial port, to another device
  Serial1.begin(19200);   // set the data rate 

}//--(end setup )---


void loop()   /****** LOOP: RUNS CONSTANTLY ******/
{
  digitalWrite(Pin13LED, HIGH);  // Show activity
  if (Serial.available())
  {
    byteReceived = Serial.read();
    
    digitalWrite(SSerialTxControl, RS485Transmit);  // Enable RS485 Transmit   
    Serial1.write(byteReceived);          // Send byte to Remote Arduino
    
    digitalWrite(Pin13LED, LOW);  // Show activity    
    delay(10);
    digitalWrite(SSerialTxControl, RS485Receive);  // Disable RS485 Transmit       
  }
  
  if (Serial1.available())  //Look for data from other Arduino
   {
    digitalWrite(Pin13LED, HIGH);  // Show activity
    byteReceived = Serial1.read();    // Read received byte
    Serial.write(byteReceived);        // Show on Serial Monitor
    delay(10);
    digitalWrite(Pin13LED, LOW);  // Show activity   
   }  

}

druhy

#include <SoftwareSerial.h>

SoftwareSerial mySerial(3, 4); // RX, TX

#define SSerialTxControl 9
   
int byteReceived;
int byteSend;

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  pinMode(SSerialTxControl, OUTPUT); 
  mySerial.begin(9600);
  digitalWrite(SSerialTxControl, LOW);
}

void loop() { 
  if (mySerial.available())
  {
    byteReceived = mySerial.read();
    Serial.write(byteReceived);          // Send byte to Remote Arduino     
  }

  if (Serial.available())
  {
    byteReceived = Serial.read();
    
    digitalWrite(SSerialTxControl, HIGH);  // Enable RS485 Transmit   
    mySerial.write(byteReceived);          // Send byte to Remote Arduino
    delay(10);
    digitalWrite(SSerialTxControl, LOW);  // Disable RS485 Transmit       
  }
}