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AUTOMATION & ROBOTICS
HOW A 10BASE-T1L MAC-PHY SIMPLIFIES LOW POWER PROCESSOR ETHERNET CONNECTIVITY
This article from Maurice O’Brien, strategic marketing manager, and Volker E. Goller, systems application engineer, Analog Devices, explains how to connect to an increased number of low power field or edge devices with a 10BASE-T1L MAC-PHY. It will also detail when to use the MAC-PHY vs. a 10BASE-T1L PHY and how these systems meet the requirements of tomorrow’s Ethernet-connected manufacturing and building installations.
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ingle-pair Ethernet 10BASE-T1L use cases, including Ethernet-APL, continue to expand across process, factory, and building automation applications driven by
the requirement to connect more devices to Ethernet networks. With more devices connected, richer datasets are made available to the higher level management systems, leading to significant increases in productivity while reducing operating costs and energy consumption. The vision of Ethernet to the field or edge is to connect all sensors and actuators to a converged IT/OT network. To achieve this vision there are system engineering challenges, as some of these sensors are limited in power and space. There is a growing market of low power and ultra low power microcontrollers with significant internal memory capabilities for sensor and actuator applications. But most of these processors have one thing in common - with no integrated Ethernet MAC, they do not support an MII, RMII, or RGMII media independent (Ethernet) interface. A traditional PHY cannot be connected to these processors.
WHY USE A 10BASE-T1L MAC-PHY To enable long range Ethernet connectivity to an increased number of lower power devices, a 10BASE-T1L MAC-PHY is required. With a 10BASE- T1L MAC-PHY, Ethernet connectivity is provided to a processor via SPI, reducing the burden on the processor by removing the need for an integrated MAC. The MAC functionality is now integrated directly with the 10BASE-T1L PHY. A 10BASE-T1L MAC-PHY provides device architects increased flexibility and choice by enabling a variety of ultra low power processors. By optimising the application partitioning, a 10BASE-T1L MAC-PHY enables lower power field devices for Zone 0 intrinsically safe deployment through what is referred to in the process industry as Ethernet- APL. Within intelligent building applications, a MAC-PHY will enable more lower power devices to be connected to an Ethernet network. Intelligent building applications include HVAC systems, fire safety systems, access control, IP cameras, elevator systems, and condition monitoring.
10BASE-T1L MAC-PHY ADVANCED PACKET FILTERING The integration of the MAC functionality with a 10BASE-T1L PHY provides new features to optimise Ethernet traffic on the network. A 10BASE-T1L MAC-PHY with advanced packet filtering will significantly reduce the overhead of
Figure 1. A 10BASE-T1L MAC-PHY significantly reduces the power and complexity of devices with advanced packet filtering.
handling broadcast and multicast traffic, while freeing the processor from this task. To filter by the destination MAC address is key. Instead of just a single MAC address, a MAC-PHY can support filtering using up to 16 unicast or multicast MAC addresses. In addition, address masking is supported for two MAC addresses. This gives a great degree of freedom, filtering for the device address as well as commonly supported multicast addresses such as LLDP (Link Layer Discovery Protocol). By supporting an additional queue for higher priorities, some messages can be prioritised and therefore get improved latency and robustness. The priority of a frame can be
identified by the MAC filtering table. For example, broadcast messages can be fed into a lower priority queue and unicast into the higher priority queue to prevent the receiver from being overloaded by a broadcast storm or traffic surge. These MAC-PHY filtering features enable netload robust devices. Frame statistics are also gathered by the MAC to assist in monitoring the network traffic and the quality of the link (see Figure 1). The MAC in the MAC-PHY also supports IEEE 1588, and therefore 802.1AS time synchronisation as required in process automation. The MAC-PHY provides support for a synchronised counter, time-stamping of received messages and time-stamp capture for transmit messages. This greatly reduces the complexity of the software design, as there is no further hardware support needed to implement time synchronisation beyond the MAC-PHY itself. The MAC can generate an output waveform timed to the synchronised counter, which may be used to synchronise external application-level operations. The SPI interface supports the Open Alliance 10BASE-T1x MAC-PHY Serial Interface. The Open Alliance SPI is a new and very effective SPI protocol designed specifically for use with a MAC-PHY.
WHEN TO USE A 10BASE-T1L MAC-PHY AND A 10BASE-T1L PHY
Both a 10BASE-T1L PHY and a 10BASE-T1L MAC- PHY bring significant advantages in different use cases. For power critical applications, a 10BASE- T1L MAC-PHY enables lower system power by
Figure 2. Comparison of the advantages of a MAC-PHY vs. a PHY for 10BASE-T1L connectivity. 10 JULY/AUGUST 2023 | FACTORY&HANDLINGSOLUTIONS
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