EtherCAT Communication Guide for APR System

Version: APR-2026.01 | TwinCAT: 3.1 Build 4024.65

PDO/SDO mapping and CiA-402 protocol reference for HIWIN E1 drives.

Overview

This skill covers EtherCAT communication architecture for the APR dual-axis linear motor system, including process data exchange (PDO), service data access (SDO), and the CiA-402 drive profile standard.

Communication Architecture

code

┌─────────────────────────────────────────────────────────────────┐
│                    Communication Layers                          │
├─────────────────────────────────────────────────────────────────┤
│  ┌──────────────┐                                               │
│  │   TwinCAT    │                                               │
│  │   PLC/NC     │                                               │
│  └──────┬───────┘                                               │
│         │                                                        │
│         ▼                                                        │
│  ┌──────────────┐    Cyclic (Real-time)                        │
│  │     PDO      │◄──────────────────────► Process Data          │
│  │  (Fast I/O)  │    Every cycle (1ms)                          │
│  └──────────────┘                                               │
│                                                                  │
│  ┌──────────────┐    Acyclic (Mailbox)                         │
│  │     SDO      │◄──────────────────────► Parameter Access      │
│  │ (Parameters) │    On-demand                                  │
│  └──────────────┘                                               │
│                                                                  │
│  ┌──────────────┐                                               │
│  │  CiA-402     │    Profile Standard                           │
│  │   Profile    │    Motion Control Objects                     │
│  └──────────────┘                                               │
└─────────────────────────────────────────────────────────────────┘

PDO vs SDO

Feature	PDO	SDO
Full Name	Process Data Object	Service Data Object
Purpose	Real-time control/feedback	Parameter configuration
Timing	Every EtherCAT cycle	On-demand (async)
Speed	Fast (μs level)	Slow (ms level)
Use Case	Position, velocity, status	Setup, diagnostics

PDO (Process Data Object) - Big Picture

PDO is the "real-time data packet" exchanged every EtherCAT cycle (e.g., 1ms)

•Think of EtherCAT as having a "delivery truck" every 1ms
•PDO is what you load into that truck: control word, target position, actual position, status...
•Fast, fixed length, exchanged every cycle

SDO (Service Data Object) - Big Picture

SDO is like a "settings/parameter" service channel

•Used to change: max velocity, acceleration limits, following error threshold, PDO mapping...
•Slow, not every cycle, typically used at startup/tuning/maintenance
•For example, locking Drive's Max profile velocity is often done via SDO once

CSP vs CSV Mode Selection

For APR system (4.2m travel, 9.7 m/s max, ≥1m constant velocity zone):

CSP (Cyclic Synchronous Position) is recommended because:

•Precise distance control for constant velocity zone
•Better multi-axis synchronization
•Easier trajectory planning (position points)
•Direct following error protection

Mode	Code (0x6060)	Command Object	Use Case
CSP	8	0x607A Target Position	Position trajectory
CSV	9	0x60FF Target Velocity	Speed control

Why CSP for Your Application

•Guaranteed constant velocity distance ≥ 1m: CSP gives "next position point every cycle" - constant velocity is naturally achieved with fixed Δpos/cycle
•Reach 9.7 m/s within 4.2m: CSP lets you calculate "accel/const/decel" distance allocation directly
•Dual-axis synchronization: CSP is more intuitive for multi-axis sync, phase lock, following error protection

Minimum Required PDO Mapping (CSP)

RxPDO (Master → Drive)

Object	Name	Type	Purpose
0x6040	Controlword	UINT16	State machine control
0x6060	Modes of Operation	INT8	Set CSP (=8)
0x607A	Target Position	INT32	Position command (inc)
0x60B2	Torque Offset	INT16	Optional: feed-forward

TxPDO (Drive → Master)

Object	Name	Type	Purpose
0x6041	Statusword	UINT16	State feedback
0x6064	Position Actual Value	INT32	Position feedback (inc)
0x606C	Velocity Actual Value	INT32	Velocity feedback
0x6061	Modes of Op Display	INT8	Confirm CSP active

Recommended Diagnostic PDO

Strongly Recommended (Debug Essential)

Object	Name	Direction	Purpose
0x603F	Error Code	Tx	First-look fault diagnosis
0x60FD	Digital Inputs	Tx	Limit/Home switch status
0x6077	Torque Actual Value	Tx	Load/friction monitoring

Optional (Enhanced Control)

Object	Name	Direction	Purpose
0x607F	Max Profile Velocity	Tx	Verify speed limit
0x60F4	Following Error Actual	Tx	Real-time error

DC Synchronization

Free Run vs DC Sync0

Mode	Description	Use Case
Free Run	Async, PDO interval ≥250μs	Simple applications
DC Sync0	Synchronized clocks	Multi-axis (recommended)

For dual-axis LMSA13L: Use DC Sync0 for precise synchronization.

DC Configuration in TwinCAT

•EtherCAT Master → Advanced Settings → Distributed Clocks
•Enable DC for each slave
•Set Sync0 cycle time = NC Task cycle (e.g., 1ms)

Unit Conversion (Critical)

PDO position values are in increments (inc), not mm.

Calibration Procedure

•Jog axis at low speed for known distance (e.g., 100mm)
•Read 0x6064 delta (actual increments)
•Calculate: inc_per_mm = delta_inc / 100
•Configure NC scaling factor

Important Objects

Object	Unit	Notes
0x607A	inc	Target position
0x6064	inc	Actual position
0x60FF	inc/s	Target velocity
0x607F	inc/s	Max velocity limit
0x6083	inc/s²	Acceleration

Object Dictionary Structure

In EtherCAT (CoE = CANopen over EtherCAT), each slave has a built-in "data dictionary":

Field	Description
Index (16-bit)	Main category, e.g., 0x6040
SubIndex (8-bit)	Sub-item, e.g., 0x6040:01
Name	Parameter name, e.g., Controlword
Access	Permission: R=Read, W=Write
Type	Data type (UINT, DINT...)

ESI File Management

Import Procedure

•Copy HIWIN_MIKROSYSTEM_ED1F_20250107.xml to: C:\TwinCAT\3.1\Config\Io\EtherCAT\
•Keep only ONE version (avoid conflicts)
•TwinCAT → I/O → Devices → Reload Device Descriptions
•Scan for devices

Troubleshooting

•"Device not found" → Check ESI file location
•Version mismatch → Remove duplicate ESI files
•Wrong PDO mapping → Verify ESI matches firmware

Available References

•references/pdo-sdo-cia402.md - Comprehensive explanation of PDO, SDO, CiA402 relationships
•references/dc-synchronization.md - Free Run vs DC synchronization concepts
•references/can-canopen.md - CAN bus and CANopen differences
•references/nq-ec8l-esi.md - Keyence NQ-EC8L ESI configuration reference
•references/nq-ec8l-xml-analysis.md - Complete XML analysis of NQ-EC8L ESI