The use cases for single-pair Ethernet 10BASE-T1L, including Ethernet-APL, are becoming increasingly numerous in the process, factory and building automation sector, as more and more devices need to be connected to Ethernet networks. If more devices are given a network connection, the higher-level management systems can be provided with more extensive databases, which on the one hand allows considerable increases in productivity and on the other hand reduces operating costs and energy consumption.

For the field or edge area, Ethernet offers the prospect of connecting all sensors and actuators to a converged IT/OT network (information technology and operational technology). To realize this vision, however, a number of system-related challenges need to be overcome, as some of the sensors in question are limited in terms of available power and space requirements. For sensor and actuator applications, there is a growing range of low-power and ultra-low-power microcontrollers with large internal memory capacity. However, the majority of these processors have in common that they do not support an MII, RMII or RGMII Media Independent (Ethernet) interface due to the lack of an integrated Ethernet MAC.

A traditional PHY can therefore not be connected to these processors.

What are the advantages of a 10BASE-T1L MAC-PHY?

A 10BASE-T1L MAC-PHY is required to equip more and more low-power devices with an Ethernet connection suitable for long distances. This module establishes the Ethernet connection of the processor via SPI. The latter is thus relieved because no integrated MAC is required, as the MAC functionality is now integrated directly into the 10BASE-T1L PHY. A 10BASE-T1L MAC-PHY therefore gives device developers more flexibility and choice, as a large number of ultra-low-power processors can be considered. By optimally partitioning the application, a 10BASE-T1L MAC-PHY allows the realization of low-power field devices for intrinsically safe Zone 0 applications. This is where what is known in the process industry as Ethernet-APL comes into play. In intelligent building applications, a MAC-PHY allows a large number of low-power devices to be connected to an Ethernet network.

Advanced packet filtering

Figure 1: A 10BASE-T1L MAC-PHY significantly reduces the power consumption and complexity of devices with advanced packet filtering.

© Analog Devices

The integration of MAC functionality in a 10BASE-T1L PHY provides new features that can be used to optimize Ethernet traffic in the network. A 10BASE-T1L MAC-PHY with extended packet filtering considerably reduces the effort involved in handling broadcast and multicast traffic. The decisive factor is filtering according to the destination MAC address. Instead of filtering according to just one MAC address, a MAC-PHY supports filtering using up to 16 unicast or multicast MAC addresses. Address masking for two MAC addresses is also possible. Filtering according to the device address and generally supported multicast addresses such as LLDP (Link Layer Discovery Protocol) provides a high degree of freedom. By supporting an additional path for higher priorities, it is possible to prioritize some messages in order to improve latency and operational reliability. The priority of a frame can be identified using the MAC filter table. For example, broadcast messages can be sent to a queue with a lower priority, while unicast messages go to those with a higher priority. This prevents the receiver from being overloaded by a broadcast storm or a short-term traffic peak. These filter functions of the MAC-PHY enable the realization of devices that are robust in terms of network load. The MAC also collects frame statistics to help monitor network traffic and connection quality (see Figure 1).

The MAC in the MAC-PHY also supports IEEE 1588 and thus also time synchronization according to 802.1AS, as required in process automation. The MAC-PHY also supports a synchronized counter, timestamping of received messages and timestamp capture for messages to be sent. This significantly reduces the complexity of the software design, as no hardware support is required beyond the MAC-PHY to implement time synchronization. The MAC can generate an output signal aligned with the synchronized counter, which can be used to synchronize external processes at the application level. The SPI interface supports the Open Alliance 10BASE-T1x MAC-PHY Serial Interface. The Open Alliance SPI is a new, highly effective SPI protocol developed specifically for use with a MAC-PHY.

10BASE-T1L MAC-PHY or 10BASE-T1L PHY?

A 10BASE-T1L PHY and a 10BASE-T1L MAC-PHY offer significant advantages in different applications. If power consumption is an issue, a 10BASE-T1L MAC-PHY enables a reduction in system power consumption as it allows a more flexible choice of host processor, as ultra-low power processors without an integrated MAC can also be considered. If the Ethernet connection is to be retrofitted to an existing device, a 10BASE-T1L MAC-PHY offers the option of continuing to use the existing processor by implementing the Ethernet connection via the SPI port. It is then not necessary to switch to a more powerful processor with an integrated MAC.