When it comes to reliable, long-distance communication protocols, RS-485 has stood the test of time. Industrial automation is one of many industries that still rely on this tried-and-true protocol, despite the rise of modern alternatives such as Ethernet, Gigabit Multimedia Serial Link (GMSL
), and low-voltage differential signaling (LVDS).
The new Core Interface blog series will explore industrial automation technology (IAT) such as building automation, process control, instrumentation, fleet management, and more, beginning with a four-post mini-series exploring what exactly has given the RS-485 communication protocol such staying power. First, we'll showcase key features and benefits of RS-485 in IAT and beyond. Later, we’ll touch on some unique use cases and highlight ADI solutions that leverage RS-485 to add value for our customers.
The RS-485 protocol remains a staple in industries that prioritize stability, longevity, and proven performance over cutting-edge technologies. This robust, cost-effective, and established protocol is naturally attractive to industries that are conservative about adopting new standards, such as:
The RS-485 standard, also known as TIA/EIA-485, enables robust performance in environments prone to electrical noise over long distances—hence its popularity for industrial and commercial applications. This immunity to noise is one of the protocol’s core strengths, but it offers many advantages besides.
RS-485 transmits and receives data using two wires carrying equal but opposite signals. Any external noise typically affects both lines equally as long as the wires are close together with matched impedances.
Balanced differential signaling improves noise immunity by canceling out interference that is common to both lines. The receiving end only reads the difference between the two signals, ignoring any noise. This ensures reliable communication even in electrically noisy environments such as factories where motors and other equipment can often generate electro-magnetic interference.
RS-485 supports both full-duplex and half-duplex communication. In full-duplex, data can be transmitted and received simultaneously, but it requires two pairs of wires. Half-duplex, on the other hand, uses a single pair of wires for both transmission and reception, alternating between the two. This makes RS-485 highly versatile, allowing engineers to choose the best mode for their application’s needs.
Standard RS-485 can support up to 32 transceivers on a single bus (or as high as 256 nodes with modern transceivers). This capability makes it ideal for multi-device communication networks in systems like factory automation or building controls, where several devices need to communicate over a single bus.
Another vital feature of RS-485 is its wide common-mode range. The system can tolerate a voltage difference of at least -7V to +12V between the grounds of devices on the same bus. This resilience ensures stable communication across devices that may not share a common ground or are subject to differing electrical potentials, which can be common in industrial setups.
Standard RS-485 can support data rates up to 10 Mbps over short distances and slower speeds over longer distances (up to 1.2 km). This makes it suitable for applications that require different combinations of speed and range.
RS-485 remains a cost-effective choice compared to modern alternatives like Ethernet, GMSL, and LVDS. Although these newer protocols offer higher data rates and more advanced features, RS-485 provides an excellent balance of performance and cost for many industrial applications. Below is a rough comparison of nodes for different technologies. As you can see, while Ethernet, GMSL, and LVDS excel in high-speed data transfer, their higher node costs and shorter transmission ranges limit their suitability for industrial systems with longer-distance, lower-data-rate needs.
Although modern alternatives offer certain advantages, RS-485 remains a key player in many industrial applications due to its balance of reliability, simplicity, and cost-effectiveness. Its wide adoption across industries like automation, building control, and motion systems is a testament to its staying power.
With features like noise immunity, long-distance communication, and support for multiple transceivers, RS-485 provides an excellent solution for environments where stability and robustness are paramount. Pair this with innovative features from Analog Devices, Inc. (ADI)’s portfolio of transceivers that push RS-485 beyond the standard, and you have a robust solution for your connectivity needs.
Next month in the RS-485 blog series, we’ll look at how extending the common mode range can increase the robustness of your bus.
