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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:

Connecting Arduino to the TTL to RS422 module.
Programming Arduino to receive data from the TTL to RS422 module.
Programming Arduino to send data to the TTL to RS422 module.
Sending data between your PC and Arduino through RS422 bidirectionally.

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	×	(Recommended) Screw Terminal Block Shield for Arduino Uno
1	×	(Recommended) Breadboard Shield For Arduino Uno
1	×	(Recommended) Enclosure For Arduino Uno

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

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

To read data come from RS422, you can use the following functions:

To write data to RS422, you can use the following functions:

And more functions to use with RS422 in Serial reference

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.

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See Also

Arduino - SoftwareSerial

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