Ethernet for Control Automation Technology (EtherCAT)

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Ethernet for Control Automation Technology (EtherCAT®) is an Ethernet-based field bus system. It is an open technology covered under international standards (IEC61158, 61784, 61800, and ISO 15745)

Introduction

• Involves controller and target(s) setup where target nodes are physically connected daisy-chain style but logically operate on a loop.

• EtherCAT specializes in precise, low jitter synchronization across target nodes (<= 1us)

• Each target processes message data “on the fly” as the frame passes from one node to the next

• Uses IEEE 802.3 Ethernet physical layer and standard Ethernet frames

Physical Network Structure

Physically: Target nodes can have multiple configurations (Line, Tree,Star, etc.)

Logically: Target nodes are connected as a daisy-chain and operate on a loop

• Duplex communication: CAT5 (Ethernet) cable has two different pairs (outgoing pair and return path)

• Only 1 Ethernet port needed at the controller to connect to network

Network Redundancy

• Requires 2nd Controller Ethernet port

• Redundant data on 2nd port (Never used unless there’s a line break)

• Loopback switches in target nodes close to maintain the loop in the event “downstream” nodes fail

Frame Structure

• 1 or more Datagrams per frame.

• Datagram consists of a Header, Data, and “Working Counter”

• Header contains:

  • Command, address, length, and various check bits

• The Working Counter (WKC) is the # of interactions contained in a given datagram.

  • WC is incremented appropriately by each target. If the WKC in the frame returned to the controller isn’t what’s expected, then there’s a problem somewhere in the network

Target Node Addressing

AutoIncrement (Position Addressing)

• Used typically only during start-up to scan the network

• Position address of the addressed target is stored as negative value

• Each target increments the address. The target that reads this address as zero is addressed

Fixed Physical (Node Addressing)

• Typically used for register access to individual targets that have already been identified

• The configured target address is assigned by the controller at start up and cannot be changed by the EtherCAT target

Broadcast Addressing (All target addressing)

• Used for initializing all target devices

• Addresses all targets in the network

Logical Addressing

• Used to reduce necessary content in process data communication

• All targets read from and write to the same logical address range of the EtherCAT datagram

• Each target uses the FMMU to map data from the logical address to the local physical memory address

Resources

ECAT Related Collateral

Foundational

• EtherCAT Device Protocol Poster - Only applicable to: F2838x, F28P65x

• EtherCAT Protocol Series - Only applicable to: F2838x, F28P65x

Getting Started

• EtherCAT User’s Guide - Only applicable to: F2838x, F28P65x

• Real-time control meets real-time industrial communications development - part 4 - Only applicable to: F2838x, F28P65x

Expert

• Design Guide: TIDM-02006 Distributed Multi-axis Servo Drive Over Fast Serial Interface (FSI) Reference Design

• EtherCAT Based Connected Servo Drive using Fast Current Loop on PMSM Application Report - Only applicable to: F2838x, F28P65x

• EtherCAT Technology Group - Download Section Landing Page - Only applicable to: F2838x, F28P65x

• Hardware Data Sheet Section I - Technology - Only applicable to: F2838x, F28P55x, F28P65x

• Hardware Data Sheet Section II - Register Description - Only applicable to: F2838x, F28P55x, F28P65x

• PHY Selection Guide - Only applicable to: F2838x, F28P65x

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