How to Use RS485 Transceiver IC: Examples, Pinouts, and Specs

The MAX485ESA, manufactured by Texas Instruments, is a low-power transceiver for RS485 and RS422 communication. This IC is designed for long-distance data transmission over differential lines and is widely used in industrial environments due to its robustness and noise immunity. Common applications include factory automation, building automation, and network communication systems.

• Voltage Supply: 4.75V to 5.25V
• Operating Temperature: -40°C to +85°C
• Data Rate: Up to 2.5Mbps
• Receiver Input Sensitivity: ±200mV
• Driver Output Voltage (Differential): ±1.5V to ±5V
• Quiescent Current (Low Power Mode): 300µA
• Number of Drivers/Receivers: 1/1
• ESD Protection: ±15kV Human Body Model

1. Power Supply: Connect VCC (Pin 8) to a 5V power source and GND (Pin 5) to the ground.
2. Differential Pair: Connect A (Pin 6) and B (Pin 7) to the differential bus lines.
3. Data Input/Output: Connect DI (Pin 4) to the transmitting data source and RO (Pin 1) to the receiving data destination.
4. Enable Pins: Control RE (Pin 2) and DE (Pin 3) to switch between receiving and transmitting modes.

• Ensure that the power supply is within the specified voltage range.
• Use termination resistors at the end of the differential bus to match the characteristic impedance and minimize reflections.
• Avoid running differential pair cables parallel to high-voltage or high-current lines to prevent noise coupling.
• Implement proper ESD protection when handling the IC to prevent damage.

• No Data Transmission: Check if the DE pin is correctly set to high to enable the driver.
• No Data Reception: Ensure the RE pin is set to low to enable the receiver.
• Data Corruption: Verify the integrity of the differential pair connection and the presence of termination resistors.

• If experiencing data loss or corruption, inspect the cable length and quality. RS485 allows for long cable runs, but excessive length can introduce signal degradation.
• Ensure that the bus is not overloaded with too many devices, which can exceed the drive capability of the transceiver.

Q: Can the MAX485ESA be used for both RS485 and RS422 communications? A: Yes, the MAX485ESA is suitable for both RS485 and RS422 applications.

Q: What is the maximum number of devices that can be connected to an RS485 bus using MAX485ESA? A: The RS485 standard allows up to 32 unit loads on the bus, but this can vary depending on the specific bus configuration and device load.

Q: How can I increase the number of devices on the bus? A: Use repeaters or RS485 transceivers with higher unit load capabilities to increase the number of devices on the bus.

#include <SoftwareSerial.h>

// Define RS485 mode pins
#define RS485Transmit    HIGH
#define RS485Receive     LOW

// Define the enable pin for MAX485ESA
#define RS485EnablePin   2

// Create a software serial port
SoftwareSerial rs485Serial(10, 11); // RX, TX

void setup() {
  // Start the built-in serial port, for debugging
  Serial.begin(9600);
  
  // Start the RS485 connection
  rs485Serial.begin(4800);
  
  // Set the RS485 mode pin
  pinMode(RS485EnablePin, OUTPUT);
  
  // Set RS485 to receive mode
  digitalWrite(RS485EnablePin, RS485Receive);
}

void loop() {
  // Check if data is available on the RS485 bus
  if (rs485Serial.available()) {
    // Read the data
    int data = rs485Serial.read();
    
    // Print the data to the debug serial
    Serial.print("Received: ");
    Serial.println(data, HEX);
  }
  
  // Check if data is available on the debug serial
  if (Serial.available()) {
    // Read the data
    int data = Serial.read();
    
    // Set RS485 to transmit mode
    digitalWrite(RS485EnablePin, RS485Transmit);
    
    // Send the data on the RS485 bus
    rs485Serial.write(data);
    
    // Delay to ensure data is transmitted
    delay(10);
    
    // Set RS485 back to receive mode
    digitalWrite(RS485EnablePin, RS485Receive);
  }
}

This example demonstrates basic sending and receiving of data over RS485 using the MAX485ESA with an Arduino UNO. The RS485EnablePin is used to switch between transmit and receive modes. Adjust the baud rate and pins according to your specific setup.