Single Pair Ethernet for Industrial Automation in Smart Factories

By Stuart Cording for Mouser Electronics

Published March 11, 2026

Manufacturers have relied on a growing range of fieldbus systems to implement their industrial automation equipment. Each has its purpose, supporting a specific range of sensors or type of communication that affords the necessary level of safety and reliability, and enables connectivity over considerable distances. Analogue systems, such as HART (4–20mA) and 0–10V, operate alongside serial buses such as CANopen, PROFIBUS, Modbus RTU, and IO-Link. Then there are the Ethernet-based options, including PROFINET, EtherCAT, Sercos III, and Modbus TCP.

But this disparate collection of connectivity is increasingly causing headaches for industrial engineering teams and plant managers because it lacks support for cybersecure communication. As Operational Technology (OT) and Information Technology (IT) become more tightly integrated, these systems become targets for cybercriminals. In the worst case, manufacturing sites can be brought to their knees, halting production for weeks or months.[1] Maintaining this fragmented collection of legacy infrastructure while complying with new regulations, such as the Cyber Resiliency Act (CRA), only adds to the complexity.

Single Pair Ethernet and New IEEE 802.3 PHYs

Given that Ethernet is used extensively, has a large code base supporting it, and integrates encryption into its communication layers, it makes sense to extend its use from IT into OT. What’s missing, and what protocols like EtherCAT and Sercos III include, is determinism for real-time control. And when considered for digital communications with sensors, the four twisted pairs of classic Ethernet clearly add unnecessary cabling and connector costs.

Single Pair Ethernet (SPE) is part of the solution that should change this. New physical layers (PHYs) in the IEEE 802.3 standard (Figure 1) enable standard Ethernet MACs on microcontrollers and system-on-chip (SoC) devices to implement SPE over a twisted pair connection (Table 1). In some cases, the technology can also meet electromagnetic compatibility (EMC) and electromagnetic interference (EMI) requirements using unshielded cables, providing room for additional cost savings.

Table 1. New SPE PHY options defined in the IEEE 802.3 standard

What is 10BASE-T1S?

The most attractive SPE addition for those working with sensors at the very edge of industrial networks is 10BASE-T1S, thanks to its support for multidrop networking. Operating at 10Mbps in half-duplex mode, it is the only multidrop SPE option. According to the specification, the compliance limit for a 10BASE-T1S is a total end-to-end segment length of 25m with a maximum of eight nodes.

However, companies such as Microchip Technology, with their aptly named 10BASE-T1S Extended Reach Demo, have shown that up to 50 nodes can be connected over 98m without detriment to signal quality (Figure 2). The IEEE has also recognised the market need for greater distance and more nodes, and is currently considering changes to define distances of 50m to 75m and 16 nodes.[2]

Further 10BASE-T1S Capabilities

To achieve reliable, deterministic data transmission, the standard also defines Physical Layer Collision Avoidance (PLCA). By dividing the network into N transmit slots, the coordinator node (typically defined as Node 0) initiates the cycle with a beacon synchronisation marker (Figure 3). Subsequently, each node can pass data, if available, in its assigned slot. This provides bounded latency to meet the needs of time-sensitive applications.

Selecting an SPE PHY for Processors with a MAC

For processing platforms with an integrated Ethernet MAC peripheral, support for SPE is as simple as integrating an appropriate PHY, such as the Microchip Technology LAN8670/1/2 10BASE-T1S Ethernet PHY Transceivers. The device can be attached to a Media Independent Interface (MII) or Reduced Media Independent Interface (RMII). They also support Carrier Sense Multiple Access/Collision Detection (CSMA/CD) as a fallback if PLCA fails.

Thanks to integrated PHY diagnostics, data can be collected to determine the cause of issues such as cable defects, shorts or opens, signal quality, and PLCA diagnostics. The available PHY devices differ in their support for the MII, SC-MII, and RMII interfaces, resulting in different pin counts for the VQFN package offered.

To enable rapid evaluation of SPE technology, an evaluation board for the LAN8670 is also available that features the RMII interface. The EVB-LAN8670-RMII Evaluation Board is ready to use with Arm-based microcontroller boards such as the SAM E54 Curiosity Ultra Dev Board (Figure 4) and the SAM E70 Xplained Ultra Evaluation Kit.

Adding 10BASE-T1S SPE to a Standard Microcontroller

An alternative approach is to broadly retain your existing industrial sensor circuit design and replace the physical interface with 10BASE-T1S SPE. This is supported by the LAN8650 and LAN8651 Single Pair Ethernet Switches. Integrating both MAC and SPE PHY, they connect to a standard microcontroller using an SPI interface that meets the OPEN Alliance 10BASE-T1x MAC-PHY Serial Interface specification.[3]

The key difference between the two devices is the inclusion of an integrated 1.8V LDO in the LAN8651, simplifying the design of systems that only have a 3.3V supply available. Event capture and generation, part of Time Sensitive Networks (TSN, IEEE 802.1AS/IEEE 1588), is also supported on the six configurable digital I/O pins.

Gaining initial experience with 10BASE-T1S SPE using the LAN8651 is made simpler thanks to a Two-Wire ETH Click evaluation board from Mikroe (Figure 5) and Microchip Technology’s software protocol driver.[4]

Ethernet Right to the Edge of Industrial Automation

The current smorgasbord of industrial communication protocols is making the lives of industrial engineers and their IT departments unnecessarily challenging. OT systems are no longer exempt from the cyber risks of the Internet, and CRA is forcing teams to evaluate the cybersecurity of industrial automation from end to end.

The emergence of SPE, coupled with support for deterministic communication and multidrop nodes, means Ethernet is well-suited to replace older analogue and digital fieldbuses that lack cybersecure protocols. Highly integrated MAC+PHY chipsets, such as the LAN8650/1, provide an opportunity to switch out existing digital protocols for 10BASE-T1S without changing their preferred microcontroller vendor, while the LAN8670/1/2 adds multidrop SPE to those microcontrollers featuring a standard Ethernet MAC with an MII or RMII interface.   

Sources

[1]https://www.bbc.com/news/articles/ckg1w255gy1o
[2]https://www.ieee802.org/3/da/public/1124/zimmerman_01_da_202411071.pdf
[3]https://opensig.org/wp-content/uploads/2023/12/OPEN_Alliance_10BASET1x_MAC-PHY_Serial_Interface_V1.1.pdf
[4]https://github.com/MicrochipTech/oa-tc6-lib

Stuart Cording is “The Electronics Reporter”—an engineer turned influencer dedicated to helping the electronics community make sense of today’s complex technologies. With 25 years of experience in semiconductors and embedded systems, he uncovers the stories, insights, and practical know-how that help engineers solve real design challenges. Through articles, podcasts, and videos, Stuart connects innovators, shares technical wisdom, and celebrates the people driving progress in deep tech.