Simplify factory automation design with multi-protocol industrial Ethernet systems

Factory automation equipment such as sensors, actuators, drives and programmable logic controllers (PLCs) support multiple industrial Ethernet protocols such as EtherCAT, Profinet, Ethernet Industrial Protocol (EtherNet/IP) and Sercos, each of which can Replacement is done by loading a different software image on the hardware platform.

Multi-protocol Industrial Ethernet systems reduce manufacturing costs during the hardware development cycle, reducing bill-of-materials costs by requiring only a single printed circuit board to be manufactured, thereby accelerating time to market. Manufacturers can use different Industrial Ethernet protocols to provide field devices for factory automation, such as digital input modules or servo drives.

Architectures such as Texas Instruments' Programmable Real-Time Unit Industrial Communications Subsystem (PRU-ICSS) are capable of supporting 1,000Mbps Industrial Ethernet rates for field devices, especially with the new Time Sensitive Networking (TSN) protocol.

Industrial Ethernet system architecture

Figure 1 shows the main components of an Industrial Ethernet field device that exchange process data with PLCs and other field devices. Two of the Ethernet ports support line or ring Ethernet topologies, which means the PLC is connected to a series of field devices via Ethernet cables without the need for an Ethernet switch.

Figure 1: Industrial Ethernet field device system block diagram

From the RJ45 connector, the media-dependent interface (MDI) connects to magnetic components that provide an isolation barrier from other devices before the Ethernet frame reaches the Ethernet physical layer (PHY) transceiver.

The PHY converts Ethernet frames to analog-to-digital (receiver) and digital-to-analog (transmitter) and passes them through the Media Independent Interface (MII), Reduced Gigabit Media Independent Interface (RGMII), or Serial Gigabit Media Independent Interface (SGMII) Outputs a digital bitstream.

The PHY plays an important role in Industrial Ethernet and is as important as the Media Access Controller (MAC). The PHY must support copper media with different pairs (single pair for T1 single-pair Ethernet, two pairs for 100Mbps Ethernet, and four pairs for 1,000Mbps Ethernet), depending on the MDI. Some Industrial Ethernet networks also support fiber optics, which have better electromagnetic compatibility (EMC) and can better withstand electromagnetic interference in harsh industrial environments.

Next, the Ethernet byte stream enters the MAC via MII. MAC is responsible for the Industrial Ethernet protocol and is an important functional block for implementing multi-protocol Industrial Ethernet support.

Since each Industrial Ethernet protocol handles Industrial Ethernet frames differently when extracting and inserting process data, the MAC handling method must vary for each protocol. Application-specific integrated circuit solutions such as MAC are often fixed to a single protocol and do not have multi-protocol capabilities. A MAC that supports multiple protocols must support multiple Ethernet frame processing methods, such as dynamic processing, cut-through forwarding, frame preemption, and store-and-forward.

The MAC transmits process data from the PLC to the central processing unit (CPU) via an interface. If the MAC is a physically separate device, the interface speed is lower (Serial Peripheral Interface (SPI) or I2C, or a memory-mapped external bus). If the MAC is integrated with the CPU, the shared high-speed memory provides this interface and synchronizes the process data between the MAC and the CPU.

The CPU performs various tasks. Each Industrial Ethernet protocol requires a software stack to interact with the MAC in order to exchange process data. Field devices use this process data to control digital inputs and outputs or control the speed and rotation of servo drives.

If the system contains multiple CPUs, it is common practice to split the workload, with the Industrial Ethernet stack running on its own CPU and the industrial applications running on other CPUs. Different kinds of operating systems (OS) can run on the CPU core: high-level operating systems (such as Linux or real-time Linux) or real-time operating systems (RTOS) (such as Free-RTOS or no-OS).

Texas Instruments Sitara™ Family of Solutions and Texas Instruments Ethernet PHYs for Multiprotocol Industrial Ethernet 

The Texas Instruments Sitara™ processor family supports programmable MACs and their integrated PRU-ICSS peripherals. The PRU loads any Industrial Ethernet protocol firmware at runtime. Sitara AM6442 As shown in Figure 2, the AM2434 and AM2434 support 1,000Mbps protocols such as TSN. The PRU-ICSS also acts as a standard Ethernet MAC and a two-port Ethernet switch.

Figure 2: Sitara AM6442 processor solution and PRU-ICSS for multi-protocol Industrial Ethernet support

The Texas Instruments Sitara™ processor family is capable of supporting multiple instances of PRU-ICSS to support position encoders (EnDAT 2.2, HIPERFACE Digital Servo Link [DSL], Bidirectional Serial Synchronization [BiSS]), pulse width modulation (PWM) and industrial peripherals such as delta-sigma decimation filters for external isolated analog-to-digital converters. Servo drives use these peripherals.

Texas Instruments Sitara™ processors also integrate functions used in industrial applications, including ADC, SPI, I2C and general-purpose memory controllers. The system-on-chip also has an internal shared memory for exchanging process data between MAC and CPU.

As shown in Figure 3, the Texas Instruments Sitara™ processor family features multiple Arm® Cortex®-A53 cores for high-level operating systems (HLOS), multiple Arm Cortex-R5F cores for RTOS or bare metal applications, and multiple Arm Cortex-R5F cores for PRU-ICSS for Industrial Ethernet MAC. 

Figure 3: Multi-core processing using RTOS, HLOS and firmware

By integrating a programmable MAC, the different frame processing methods required by multi-protocol industrial Ethernet are supported, and the application processor is placed on a single chip. An internal high-speed memory interface enables fast exchange of process data between processor and MAC, and the family offers scalable processor cores.

Texas Instruments offers evaluation modules (EVMs) for the Sitara™ processor family and Ethernet PHY solutions using the DP83867 or DP83869 Ethernet PHY transceivers.