What is RS485?
RS485 communication guide


A large number of current electronic equipment communicate with computers via serial ports. RS-485 is one of the legacy serial interfaces still widely applied these days. Extremely common in industrial automation, RS-485 is used in industrial networks, including Modbus, Profibus DP, ARCNET, BitBus, WorldFip, LON, Interbus, as well as many other non-standard networks. At present, serial RS-485 port is rightfully considered to be the most efficient way of serial communication. So, let’s find out why RS-485 communication remains that popular and what is the simplest way to monitor and test this common interface.

Contents


  1. What is RS-485?
  2. RS-485 communication: main features
  3. How to test RS-485 ports?
  4. Core functionality of RS-485 test tool
  5. How-to guide?

What is RS-485?


RS-485 (currently known as EIA/TIA-485) is a standard interface of the physical layer of communication, a signal transmission method, the 1st level of the Open System Interconnection model. RS-485 has been created in order to expand the physical capabilities of RS-232 interface.

The serial EIA-485 connection is done using a cable of two or three wires: a data wire, a wire with inverted data, and, often, a zero wire (ground, 0 V). This way, transmitters and receivers exchange data via a twisted-pair cable of 22 or 24 AWG solid wires. The main idea here is to transport one signal over two wires. While one wire transmits the original signal, the other one transports its inverse copy. Such transmission method provides high resistance to common mode interference. The twisted-pair cable that serves as a transmission line can be shielded or unshielded.

RS-485 communication: main features


Despite the wide variety of modern alternative solutions, today RS-485 technology remains the basis of many communication networks. The major advantages of RS-485 interface are:

  • Two-way data exchange via one twisted pair of wires;
  • support for several transceivers connected to the same line, i.e., the ability to create a network;
  • long length of the communication line;
  • high transmission speed.

Now, let’s take a closer look at the main characteristics of RS-485 communication:

  1. Bi-directional half-duplex data transmission. Serial data stream can be transported in one direction, data transfer to the other side requires using a transceiver. A transceiver (commonly referred to as 'driver') is a device or an electrical circuit that forms a physical signal on the transmitter side.

  2. Symmetrical communication channel. Receiving or transmitting data requires two equivalent signal wires. The wires are used to exchange data in both directions (alternatively). With the help of a twisted pair cable, the symmetrical channel significantly increases the stability of a signal and suppresses electromagnetic radiation generated by the useful signal.

  3. Multi-pointing. RS-485 communication line can work with multiple receivers and transceivers connected. At the same time, one transmitter and several receivers can be attached to one communication line at a time. All the other transmitters that need to be connected should wait until the communication line is free for data transmission.

How to test RS-485 ports with Serial Port Monitor


The EIA/TIA-485 standard is widely used in industrial applications that work over long distances and require high speeds of data transmission. The interface is particularly useful for connecting serial devices in noisy environments like process control plants, utilities sites, and factories.

RS-485 port is embedded on various devices, including low-speed modems, programmable logic controllers, computer numerically controlled machine tools, point of sale terminals, metering instruments, large special automated machines, and other equipment.

So, it should come as no surprise that specialists working with RS-485 ports may need to test the serial interfaces in order to identify and resolve problems that may appear in RS-485 networks. More than that, programmers who develop industrial serial applications may also require a specialized tool for reading and monitoring serial ports their apps communicate with.

Thankfully, there’s a dedicated RS-485 test software that is designed to make it as simple as possible to monitor and analyze RS-485 port activity. Packed with a slew of advanced features, the software doesn’t need additional hardware to track and record data going through monitored serial ports.

RS485 communication software by Eltima

Serial Port Monitor is focused on catching, logging, and displaying serial data transmitted over system’s RS-485 ports.
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Serial Port Monitor

Log and analyze serial port activity
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Serial Port Monitor

Core functionality of RS-485 test tool


The key capabilities of RS485 communication software (SPM) include:

  • Connecting to a COM port any time you need it even if the port is already used by another app. Once you start monitoring a required RS-485 interface, all data transmitted through it is shown in real time. Thanks to this option, you can timely resolve any problem that arises in your
    serial communication network.

  • Monitoring multiple COM ports at a time. Whether you need to analyze one, two, or several RS-485 ports, it’s possible to do this in one monitoring session. With that, the captured data will be saved to a single log.

  • Simulating serial communication. The Terminal mode option allows you to emulate sending particular data in different formats (string, binary, octal, decimal, hexadecimal, mixed). The RS-485 loopback feature offered by the software is particularly useful for sessions comparison.

How-to guide


Whether you need to remotely monitor a controller fitting RS-485 port, check the reaction of a particular serial device to certain data, or analyze the activity of all RS-485 interfaces your system deploys, here is how you can do this with
Serial Port Monitor:

To start, download the software and install it on your computer. Launch the app in order to start a new monitoring session:

  1. In the main menu of the app select Session -> New session. Alternatively, you can hit ‘New’ on the main toolbar or press CTRL+N. As a result, you’ll get the ‘New monitoring session’ window.

  2. Now, decide on how you’d like the captured data to be displayed and choose the desired visualizer. There are Table, Line, Dump, Terminal, and Modbus views. As an option, you can use them all simultaneously.

  3. Next, depending on where you want your monitoring session to be started, choose between the ‘Start monitoring now’ and ‘Start in new window’ options.

  4. In the ‘Capture options’ select the type of events you’d like to track (Create/Close, Read/Write, Device Control.)

  5. Finally, hit ‘Start monitoring’. That’s it! Now you can easily catch and analyze data transmitted via a required RS-485 port.

If it’s necessary to save a session, you should go to the main menu and select “Session -> Save session/Save session As”. Or, click “Save” on the main toolbar, or press CTRL+S.

Find more information what is serial loopback test and how to perfom it.

Serial Port Monitor

Requirements: Windows XP/2003/2008/Vista/7/8/10/Server 2012 , 9.16MB size
Version 7.0.342 (13th Jan, 2018) Release notes
Category: Communication Application