RS485 is a standard for serial communication that allows multiple devices to communicate over a single pair of wires. It's used in industrial environments due to its robustness and ability to cover long distances.

• check_circle Differential Signaling: RS485 uses differential signaling, which means it sends data as the difference between two voltages on a pair of wires (A and B). This helps in reducing noise and allows communication over long distances (up to 1.2 km or about 4000 feet).
• check_circle Multi-Device Communication: Up to 32 devices can be connected on a single RS485 bus.
• check_circle Half-Duplex: Communication is typically half-duplex, meaning devices take turns sending and receiving data on the same pair of wires.

1. Data Transmission

• arrow_forward When a device wants to send data, it generates a differential voltage (e.g., A = +5V and B = 0V for a binary '1', A = 0V and B = +5V for a binary '0').
• arrow_forward This voltage difference is transmitted over the twisted pair of wires.

2. Data Reception

• arrow_forward The receiving device detects the differential voltage and interprets it back into binary data.
• arrow_forward This method helps in rejecting common-mode noise because the noise affects both wires equally, and the differential receiver can cancel it out.

• lightbulb Differential Signaling: By sending the same signal as a positive voltage on one wire and as a negative voltage on another wire, RS485 can effectively cancel out noise picked up along the transmission line.
• lightbulb Common-Mode Rejection: This technique ensures that noise which affects both wires equally does not impact the signal integrity.
• lightbulb Multipoint Communication: RS485 supports multipoint communication, meaning multiple devices can share the same bus without interference, provided only one device transmits at a time.

For an Arduino with a MAX485 transceiver:

• check_circle Connect RO (Receiver Output) to Arduino RX.
• check_circle Connect DI (Driver Input) to Arduino TX.
• check_circle Connect DE (Driver Enable) and RE (Receiver Enable) to a digital pin (e.g., pin 2) to control transmission and reception.

#define DE_RE 2

void setup() {
  pinMode(DE_RE, OUTPUT);
  digitalWrite(DE_RE, LOW); // Enable receiver
  Serial.begin(9600);
}

void loop() {
  // Send data
  digitalWrite(DE_RE, HIGH); // Enable transmitter
  Serial.write("Hello RS485");
  delay(100); // Wait to ensure data is sent
  digitalWrite(DE_RE, LOW); // Enable receiver

  // Receive data
  if (Serial.available()) {
    String received = Serial.readString();
    Serial.println("Received: " + received);
  }

  delay(1000); // Wait before next transmission
}

This code switches between sending and receiving modes, ensuring no conflict on the RS485 bus.