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Pain-Free RS-485 Installation and Troubleshooting

Have you ever been tasked with setting up and configuring an RS-485 network? Have you felt the pain and frustration of trying to configure the terminators and pull high/low resistors of the network’s RS-485 nodes so the network can transmit data reliably, all the time? If so, then you may have reacted to the title of this article with a great deal of skepticism. So let me get right to the point. Moxa has developed a new technology, called “Intelligent RS-485,” that has two important and very attractive functions:

  1. One-Click RS-485 Installation
  2. One-Click RS-485 Troubleshooting

Sound too good to be true? Maybe, but let me assure you that with the right product portfolio, it’s really that simple and straightforward. Once you’ve installed the serial boards in your computer and connected the cables to the boards and the devices to the cables, you’re ready to go. You no longer need to get out your oscilloscope and/or custom-built testing device, and you don’t need to adjust pull high/low resistors on the serial boards. That’s done automatically. The “buttons” you click on are in the configuration interface software that comes with the boards.

Quick Review

RS-485 is a top choice for engineers who need to create small, private device networks for automation applications, and is used widely for industrial field applications that require stable data transmission over relatively long distances. The RS-485 serial communications standard provides better noise immunity than RS-232, allows more devices to be connected to the same data line, and supports peer-to-peer communication at distances up to 4000 feet (1200 meters) at 9600 bps.

Although RS-485 technology has a number of benefits, it often takes a seasoned expert who has several years of experience to set up and fine-tune the RS-485 network. The biggest challenge is knowing how to configure the terminators and pull high/low resistors. The fact that a test network runs without error in the laboratory in no way guarantees that it won’t fail in the field, particularly since field sites can contain any number of unexpected conditions that affect the fidelity of the network. A common scenario is that once the network is set up, an expert must be hired to go onsite to adjust the terminators and pull high/low resistors, resulting in an extra expenditure of both time and money.

Electronically, an RS-485 network is a relatively simple circuit that simultaneously transmits two signals. Labeled D+ and D-, the signals are identical except that the D+ signal has a slightly higher voltage than the D- signal. Actual RS-485 field applications are complicated by the lengths of the wires and the nature and numbers of nodes involved. Setting up an RS-485 network is relatively straightforward. The challenge comes when the power is turned on and the devices connected to the network start transmitting and receiving data. In most cases, engineers will need to further tune the system by configuring pull high/low resistors and terminators at strategic points along the network. It may even be necessary to modify the environment, since electronic devices external to the network can disrupt data flow. Three situations are commonly encountered:

  • The length of the network fits the RS-485 standard, and even though pull high/low resistors and terminators have been adjusted, communication still fails
  • The network works okay when only a few devices are connected, but cascading several RS-485 devices (10 or more, for example) causes communication failure
  • Changing the RS-485 baudrate from low to high decreases the maximum allowed cable length

Moxa’s Intelligent RS-485 technology determines if any of these situations exists, adjusts the serial boards’ hardware settings accordingly, or gives the user a status report that indicates what kind of adjustments must be made to the network before it can be successfully configured.

A Quick Peek at Using Moxa’s Intelligent RS-485 Technology

Moxa’s new patent-pending Intelligent RS-485 technology provides a user-friendly interface that makes it easy to configure an RS-485 network. Intelligent RS-485 has two essential functions: (1) One-Click RS-485 Installation automatically analyzes the network topology and then adjusts terminators and pull high/low resistors, and (2) One-Click RS-485 Troubleshooting tells you what to change to make a deficient network viable.

One-Click Installation
Pressing the “Auto-Tuning” button tells the system to automatically detect the status of the RS-485 bus and then adjust terminators and pull high/low resistors in the appropriate way

One-Click Troubleshooting
Pressing the “Start Diagnostic” button tells the system to display an error status table that indicates what adjustments need to be made to the network configuration.


Moxa’s new patent-pending Intelligent RS-485 technology was created to eliminate the hassle of setting up and tuning RS-485 networks. The technology is built into an exciting new series of advanced Moxa PCIe serial boards, giving engineers a powerful new tool that can be used to greatly simplify the task of setting up their networks.
The following new PCIe products all support Intelligent RS-485:


4-port RS-422/485 PCIe card with isolation


8-port RS-422/485 PCIe card with isolation


8-port RS-232/422/485 PCIe card with isolation


16-port RS-232/422/485 PCIe card

More Info

For additional information about Moxa’s Intelligent RS-485 technology, click download our Intelligent RS-485 white paper here.

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