Everything You Need To Know About RS485
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Everything You Need To Know About RS485

Learn how to Build, Maintain and Troubleshoot RS485 communication networks
4.8 (47 ratings)
Instead of using a simple lifetime average, Udemy calculates a course's star rating by considering a number of different factors such as the number of ratings, the age of ratings, and the likelihood of fraudulent ratings.
203 students enrolled
Created by Emile Ackbarali
Last updated 8/2016
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Current price: $10 Original price: $75 Discount: 87% off
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  • 2 hours on-demand video
  • Full lifetime access
  • Access on mobile and TV
  • Certificate of Completion
What Will I Learn?
  • Be aware of the two areas of consideration for RS485 communications
  • Understanding of communication port parameters
  • Understanding of cabling standards
  • Configure RS485 communications between a PLC and a Computer
  • Be able to effective use a USB-to-RS485 converter for connection to a Computer
  • Understand the process of serial data transmission
  • Be able to troubleshoot any RS485 based network in the field of plant automation
View Curriculum
  • Fundamentals of binary data systems and how computers store and exchange binary data

RS-485 is the de facto workhorse of data communications in the field of plant automation.

It is very effective in applications with significant electrical interference (noise) requiring a long transmission distance. Thus, the standard is often used in industrial applications. It is as an inexpensive local area network (LAN) connection that allows multiple receivers to connect within a multi drop configuration. RS-485 does not include a communications protocol.

This course delivers the theoretical and practical aspects of RS-485 in a very effective way, so that at the end, you will be able to build, maintain and troubleshoot any RS-485 based network in the plan automation field. The course features a live physical connection between a PLC and a Computer via a USB-to-RS485 converter, an example that is key to effective troubleshooting of RS-485 systems. 

After completing this course, you will be able to integrate devices from the same manufacturers and different manufacturers, that are RS-485 compliant, to form a complete seamless network.

Who is the target audience?
  • Electrical Engineers
  • Electrical Technicians
  • Electrical Tech or Engineering Students
  • Process Control Technicians
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Curriculum For This Course
40 Lectures
1 Lecture 03:20
Communication Port Parameters
9 Lectures 23:57

The four parameters are baud rate, number of data bits, number of stop bits and also parity. In addition to that, two very important rules of RS485 communications are stated.

Preview 01:29

In order to get a firm grasp of the four communication port parameters, you have to understand how data is transmitted along wires. Specifically, you have to understand a particular type of transmission know as synchronous serial transmission.

Preview 03:40

In asynchronous serial transmission, the clock signal is removed and the synchronization of bit rate is done through software settings.

Preview 01:56

The bits per second rate is known as the baud rate when talking about serial transmission. 

Preview 02:14

Each byte of data that is sent is framed by synchronization and error checking bits. Together with the data that is sent, the data stream is known as a data frame.

The Serial Data Frame

The number of data bits communication port parameter in RS485 allows the selection of either 7 or 8 bits. Many times, however, this selection is not given and the parameter is defaulted to 8 bits.

Data Bits

The start and stop bits mark the start and end of a serial data frame and is used by the receiver as such.

Start and Stop Bits

Parity is expressed by a single bit. It is a form of error checking. There can be even, odd or no parity.


We look at how two ASCII characters "OK" are transmitted serially.

An Example Real World Serial Data Stream
Communication Port Parameters in Practice
10 Lectures 23:19

A brief step by step description of the content that will be covered in the section.

What we are going to do in this Section

A look at the different physical characteristics of the Direct Logic 05 PLC.

An Overview of the Direct Logic DL05 PLC

I show you how the hardware is connected on my workbench.

The Physical Hardware Setup

Using the PLC configuration software, the communication port parameters for Port #2 on the PLC is configured.

Configuration of the DL09 PLC Port #2 Parameters

A brief description of a terminal application and what it does.

Introduction to Terminal Applications

The terminal application will receive data from the PLC via the virtual serial port on the laptop. This lecture shows how to download and install the application.

Downloading and Installing the Terminal Application

The PLC is programmed to periodically send serial data to the laptop via the serial connection. It will be programmed to send the phrase "Hello World!".

Programming the PLC to send Serial Data

The terminal application is used to view the serial data coming through the virtual serial port of the laptop from the PLC.

Viewing the Serial Data from the PLC

The baud rates are set up to be different between the PLC and the laptop. The effect of this is viewed via the terminal application. 

The Effect of Mismatched Baud Rate

One parameter at a time, the stop bits, data bits and parity are setup to be mismatched and the effect is seen via the terminal application.

The Effect of Mismatched Stop Bits, Data Bits and Parity
Live RS485 Communication to a Remote Terminal Unit device
10 Lectures 20:27

A brief step by step description of the content that will be covered in the section.

What we are going to do in this Section

The actual USB-to-RS485 converter is shown and the functions of each part is explained.

A look at the actual USB-to-RS485 Converter that will be used.

The actual physical MT-102 remote terminal unit is shown. 

A look at the actual MT-102 Remote Terminal Unit that will be used.

Via a schematic, the details of the connection of the computer to the RTU via the USB-to-RS485 converter is shown.

A Schematic of the Computer to RTU Connection

The actual physical connection between the Laptop and the MT-102 RTU is shown on the workbench.

A look at the actual Computer to RTU Connection on the Workbench

The MT-102 is configured using it's programming/configuration software. Specifically, it is set up for communication via RS485. Modbus communication is also activated on the RS485 port.

Configuration of the Communication Port Parameters on the MT-102 RTU

For the Modbus communication to be understood, details are given on the Modbus Unit ID as well as some relevant memory blocks that will be read.

Identification of Modbus Unit ID and relevant Memory Blocks

Modscan32 is set up to read memory blocks from the MT-102 RTU to show that the RS485 communication is operating as desired.

RS485 Communication using Modscan32

The Modscan32 port parameters are changed to simulate mismatched port settings, and the effect is shown.

Effect of Mismatched Port Parameters on Communication

The RS485 signal wires are interchanged to simulate a hardware connection issue and the effect on the communication is shown.

Effect of Interchanged Signal Wires on Communication
RS485 Signalling and Cabling
9 Lectures 36:50

RS485 devices are typically connected in a pattern known as Daisy Chain.

RS485 Interconnection - Daisy Chain

A comparison is made between full duplex (RS232) and half duplex (RS485) transmission.

Full Duplex vs. Half Duplex

A comparison is made between Single-Ended (RS232) and Differential (RS485) data transmission systems.

Single-Ended vs. Differential Data Transmission

Each RS485 device has a receiver and a transmitter.

RS485 Device Receiver and Transmitter Components

A look at the voltages that are used by transmitters and receivers to transport binary data.

RS485 Voltages for Binary Representation

A look at how an output can be in one of 3 states. Binary 1, Binary 0 or high impedance ... and why this is necessary.

Understanding Tri-State

Signal to Noise on a communication line is described from a very practical standpoint and the significance of it in the design of serial communications systems is emphasized.

The Significance of Signal-to-Noise Ratio

UTP cabling is used for most RS485 cabling installations. STP will be used in areas of very high EMI.

Unshielded and Shielded Twisted Pair Cabling (UTP/STP)

How the act of twisting wires together rejects noise.

Twisted Pair Noise Rejection
1 Lecture 01:31

What to do next to keep further solidify concepts.

The End - Where to go from here
About the Instructor
Emile Ackbarali
4.5 Average rating
1,035 Reviews
2,511 Students
13 Courses
Software Developer, Systems Integrator and Entrepreneur

I have been working in the fields of Software Development, Software Systems Integration and Process Automation since 1996. In 2003, I stepped out on my own and started working for myself providing software development and systems integration services to small and medium businesses.

I am also associated with a great company called Mora Systems Limited that under the leadership of it's Managing Director has produced innovative and outstanding products and services in the fields of GIS and Cellular based SCADA.

Teaching has always been a passion for me. I have taught at the tertiary level for many years on the subjects of programming, control systems as well as systems integration. In the last few years I found myself incorporating more and more videos into the curriculum with amazing results.

When I heard of uDemy I just could not help but sign up. With teaching in a classroom, you can reach only so many students, but with uDemy you can reach the world! I plan to publish and promote as many courses as I possibly can on the uDemy platform.