A test using the Teensy 3.1 to Sparkfun RS485 breakout to RS485 converter

SerialRS485TestTeensy.ino

/**
 * Wiring 
 * ------------------------------------------
 * Teensy Pin 0 RX1 ==> RS485 Breakout TX-0 
 * Teensy Pin 1 TX1 ==> RS485 Breakout RX-1
 * Teensy Pin 2  ==> RS485 Breakout RST
 * Teensy GND  ==> RS485 Breakout GND and G
 * Teensy VIN  ==> RS485 Breakout 3-5V
 * 
 * RS485 Breakout GND => RS485 Breakout  G
 * RS485 Breakout A ==> RS485 converter RX+ And TX+ 
 * RS485 Breakout B ==> RS485 converter RX- And TX- 
 * 
 * RS485 converter RX- => TX- 
 * RS485 converter RX+ => TX+
 */

int RS485RTS = 2 ; 
int RS485ActivityPin = 13 ; 

#define RS485_SEND LOW
#define RS485_RECV HIGH

// set this to the hardware serial port you wish to use
#define HWSERIAL Serial1

void setup() { 
  pinMode(RS485ActivityPin, OUTPUT);
  
  Serial.begin(9600);
  HWSERIAL.begin(9600);  
  HWSERIAL.transmitterEnable(RS485RTS); 
  
  digitalWrite(RS485ActivityPin, HIGH);
  Serial.println("hello world v14"); 
  HWSERIAL.println("hello world v14"); 
  digitalWrite(RS485ActivityPin, LOW);
}

void loop() {
  int incomingByte;
        
  if (Serial.available() > 0) {
    digitalWrite(RS485ActivityPin, HIGH);
    
    incomingByte = Serial.read();
    
    Serial.print("USB-FYI: USB received: " );
    Serial.println(incomingByte);
    HWSERIAL.print("HWS-FYI: USB received:");
    HWSERIAL.println(incomingByte);
    
    digitalWrite(RS485ActivityPin, LOW);
  }
  if (HWSERIAL.available() > 0) {
    digitalWrite(RS485ActivityPin, HIGH);
    
    incomingByte = HWSERIAL.read();
    Serial.print("USB-FYI: UART received: ");
    Serial.println(incomingByte);
    HWSERIAL.print("HWS-FYI: UART received:");
    HWSERIAL.println(incomingByte);

    digitalWrite(RS485ActivityPin, LOW);
  }

  static unsigned long previousMillis = 0;        // will store last time LED was updated
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= 1000 ) {
      // save the last time you blinked the LED
      previousMillis = currentMillis;

      static unsigned int count = 0 ; 
      count++;

      digitalWrite(RS485ActivityPin, HIGH);
      
      Serial.print("USB-FYI: count: ");
      Serial.println(count);
      HWSERIAL.print("HWS-FYI: Ucount:");
      HWSERIAL.println(count);
      
      digitalWrite(RS485ActivityPin, LOW);
  }
}