Arduino RS422

In this guide, we will delve into how to set up RS422 communication with Arduino. We'll go through the following steps thoroughly:

The tutorial also provides the instruction for both Hardware Serial and SoftwareSerial.

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×TTL to RS422 Module
1×Jumper Wires
1×(Optional) RS422 to USB Cable
1×(Optional) 9V Power Adapter for Arduino
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Optional) Transparent Acrylic Enclosure For Arduino Uno

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
Please note: These are Amazon affiliate links. If you buy the components through these links, We will get a commission at no extra cost to you. We appreciate it.

About TTL to RS422 Module

When utilizing serial communication on Arduino through functions like Serial.print(), Serial.read(), and Serial.write(), the Arduino transmits data via the TX pin and receives data through the RX pin. These pins operate at TTL level, meaning the signals they handle have limited range. Thus, for serial communication over longer distances, it becomes necessary to convert the TTL signal to RS232, RS422, or RS422 signal standards.

In this tutorial, we'll delve into the utilization of RS422 (also known as RS-422) with Arduino by employing a TTL to RS422 module. This module facilitates the conversion of TTL signals to RS422 signals and vice versa.

Pinout

The RS422 to TTL module has two interfaces:

  • The TTL interface (connnected to Arduino) includes 4 pins
    • VCC pin: power pin, needs to be connected to VCC (5V, or 3.3V)
    • GND pin: power pin, needs to be connected to GND (0V)
    • RXD pin: data pin, needs to be connected a TX pin of Arduino
    • TXD pin: data pin, needs to be connected a RX pin of Arduino
  • The RS422 interface comprises the following pins:
    • A (R+) pin: RX+ pin of the module, connect this pin to TX+ pin (T+ or Y pin) of the other RS422 device.
    • B (R-) pin: RX- pin of the module, connect this pin to TX- pin (T- or Z pin) of the other RS422 device.
    • Y (T+) pin: TX+ pin of the module, connect this pin to RX+ pin (R+ or A pin) of the other RS422 device.
    • Z (T-) pin: TX- pin of the module, connect this pin to RX- pin (R- or B pin) of the other RS422 device.
    RS-422 module Pinout
    image source: diyables.io

Wiring Diagram

  • Wiring diagram if using hardware serial
Arduino TTL to RS422 Wiring Diagram

This image is created using Fritzing. Click to enlarge image

  • Wiring diagram if using software serial
Arduino RS-422 to TTL Wiring Diagram

This image is created using Fritzing. Click to enlarge image

How To Program Arduino to use the RS422 module

  • Initializes the Serial interface:
Serial.begin(9600);
  • If you use SoftwareSerial, you need to include the library and declare a SoftwareSerial object:
#include <SoftwareSerial.h> // Define the SoftwareSerial objects and their pins SoftwareSerial rs422(6, 7); // RX: 6, TX: 7

Arduino Code for Hardware Serial

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rs422 */ void setup() { // start communication with baud rate 9600 Serial.begin(9600); // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on Serial if (Serial.available()) { char data = Serial.read(); // read the received character Serial.print(data); // echo back to data to the sender } }

Arduino Code for Software Serial

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rs422 */ #include <SoftwareSerial.h> // define the SoftwareSerial object and their pins SoftwareSerial rs422(6, 7); // RX: 6, TX: 7 void setup() { // start communication with baud rate 9600 rs422.begin(9600); // wait a moment to allow serial ports to initialize delay(100); } void loop() { // Check if there's data available on rs422 if (rs422.available()) { char data = rs422.read(); // read the received character rs422.print(data); // echo back to data to the sender } }

Testing

You can do a test by sending data from your PC to Arduino via RS-422 and vice versa. To do it, follow the below steps:

  • Connect Arduino to your PC via RS422-to-USB cable as below:
Arduino RS422 to PC communication
  • Install a Serial Terminal Program like Tera Term or PuTTY
  • Open the Serial Terminal Program and configure the Serial parameters (COM port, baurate...)
  • Type some data from the Serial Termial to send it to Arduino.
  • If successful, you will see the echo data on the Serial Terminal.

Video Tutorial

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