01 Slave hardware design

Minimum Slave System

The minimum system of EtherCAT is composed of MCU, ESC, crystal oscillator, EEPROM, PHY chip and RJ45 interface.

Slave application system

Generally speaking, we can use MCU + ESC chips, integrated IO control and motor control two slave solutions. When applying as an IO slave, you can use the on-board 4 LEDs and 4 Buttons to implement the IO logic function. As a Motor slave application, the BLDC motor can be driven using UVW and HALL sampling circuits. In addition, it can also introduce extended interfaces such as ADC, DAC, CAN and RS485.

02 Slave software design

Slave stack code

Code structure

The code structure of EtherCAT Slave Stack Code is shown in the figure below, including ESC memory interface, mailbox (CoE, EoE, etc.), DC (Sync) synchronization function, process data processing, state machine and local communication applications. The processing of process data uses an object dictionary, which is consistent with the definition of the CoE protocol.

The basic sample code is available from the official SSC Tool.

State Machine

The EtherCAT state machine (ESM, EtherCAT Slave Machine) is responsible for coordinating the state relationship between the master and slave applications at initialization and runtime. The ESM in the SSC code is implemented in the AL_ControlInd() function. The EtherCAT device must support four states, and there is an optional state. All state changes are initiated by the master station. For details, you can see the application layer protocol specification of "ETG.1000-part 6".

ESI slave information interface file

EEPROM content structure

ESC uses EEPROM to store required device-related information, called Slave Information Interface. The capacity of EEPROM is 1Kbit ~ 4Mbit, depending on the ESC specification. The content structure of EEPROM is shown in the figure below. Use the word address, and the words 0~63 are essential basic information. All of this information is written in the XML file.

XML file structure

Each slave must have an XML configuration file. The object dictionary and PDO settings defined in XML need to correspond to the object dictionary in firmware. Remember the slave information file xml file mentioned in "Overview". Several parts marked with blue are the main configuration content.

The following figure is a view converted by the XML editor. The key object dictionary and data types are in the Devices->Device->Profile element. The above part is manufacturer information, and the following part is slave description information, including device identification, device name, interface type, FMMU channel, SM, process data definition, mailbox, distribution clock, and EEPROM.