Bonfiglioli Vectron EM-SYS System Bus Expansion Module Networking and Virtual Link Configuration Guide

In modern industrial automation, multi axis synchronization and distributed control are key to improving equipment performance. Bonfiglioli provides the EM-SYS system bus extension module for the ACTION and ACTION Cube series frequency converters, which is based on CAN (Controller Area Network) technology to achieve real-time data exchange between frequency converters and between frequency converters and the upper control system.

This article will delve into the hardware installation of the EM-SYS module, CANopen protocol stack application, network management (NMT), SDO/PDO channel configuration, and the core "virtual link" mapping mechanism, providing engineers with a complete reference for networking and debugging techniques.

Chapter 1: EM-SYS Hardware Installation and CAN Bus Physical Layer

The EM-SYS module serves as a system bus expansion component for the frequency converter and is installed in the lower slot of the device.

1.1 Key points for safe assembly

According to the guidelines in Chapter 3 of the manual, the assembly process must strictly follow the following safety steps:

Power off operation: The module installation can only be carried out after the inverter completely cuts off the power and waits for the DC bus capacitor to discharge completely. This is the primary prerequisite for preventing electric shock and equipment damage.

Module insertion: The EM-SYS module is pre installed in the housing, and touching the exposed PCB board on the back is prohibited to prevent electrostatic discharge (ESD) from damaging the components. Align the module with the lower slot and insert it smoothly until it is fully seated.

Cover plate reset: After installation, the lower cover plate needs to be reinstalled in place. After the frequency converter is powered on again, the EM-SYS module automatically enters the ready state.

1.2 CAN Bus Terminal Resistance Configuration

The CAN bus requires terminal resistors to be configured at the first and last nodes of the physical bus to eliminate signal reflections. The EM-SYS module provides flexible terminal configuration options:

DIP switches S1 and S2 (Chapter 4.1):

Passive terminal: Set S1 to ON and S2 to OFF. This is a standard 120 ohm terminal configuration.

Active terminal: Set both S1 and S2 to ON. Active terminals improve signal edge characteristics through bias circuits, making them particularly suitable for long-distance or high interference environments.

Key principle: Active terminals are only allowed to be activated at one point on the bus, and passive terminals must be used for all other terminal nodes. Both S1 and S2 are set to OFF by default at the factory.

1.3 Cable specifications and wiring definitions

Cable type: Twisted pair cables with braided shielding layers must be used, and the use of aluminum foil shielding layer cables is strictly prohibited.

Terminal X410B (Chapter 4.3):

Terminal 4: CAN_GND (signal ground)

Terminal 5: CAN_Low (CAN low line)

Terminal 6: CAN-High (CAN high wire)

Terminal 7: PE (shielded grounding)

Shielding treatment: The shielding layer needs to be connected to the PE (protective ground) with a large area and low impedance at both ends, which is the key to meeting EMC compliance.

Chapter 2: System Bus Protocol Stack and Network Management (NMT)

The system bus protocol of EM-SYS is based on the CANopen (CiA DS 301) standard and adopts a message oriented communication mechanism. Understanding its network management model is the foundation of networking.

2.1 Node Address and Baud Rate Setting

Node ID (Node-ID 900) (Chapter 4.5): Values range from 1 to 63, and each node's address on the bus must be unique.

Node ID=-1 (factory default): The system bus function is turned off.

Node ID=0: Define the frequency converter as the system bus master station. Only one main station is allowed in the entire network.

Baud Rate 903 (Chapter 4.4): The baud rate of all nodes must be consistent, which determines the maximum bus length:

50 kbps → 1000 meters

250 kbps → 250 meters

1000 kbps → 25 meters

2.2 NMT State Machine and Startup Sequence

CANopen defines three NMT states (Sections 4.7, 4.8.1):

Pre Operational: The default state after power on initialization. At this time, only SDO (Parameter Data) communication is allowed, PDO (Process Data) is prohibited.

Operational: PDO communication is activated to achieve real-time data exchange. Meanwhile, SDO can still be accessed.

Stopped: All communication is prohibited.

Main station startup process:

After the main station is powered on and initialized, it needs to wait for a configurable delay time (Boot Up Delay 904, default 3500ms) to ensure that all slave stations complete initialization. Subsequently, the master station sends the NMT command Start Remote Node (command word 0x01, node ID 0x00 represents broadcast) to switch all slave stations from Pre Operational to Operational state, and PDO data exchange begins immediately.

2.3 Emergency message and main station fault response

When a fault occurs at the slave station, an Emergency Message will be sent (Chapter 4.8.3, 4.9.3). The behavior of the main station is determined by the parameter Emergency Reaction 989:

989=0 (Error): After receiving an emergency message, the master station also enters a fault state and reports fault code F21nn (nn is the hexadecimal node ID of the faulty slave station). Meanwhile, the warning bit Sysbus (0x2000) is set.

989=1 (No Error): The main station only displays a warning and does not trigger its own fault.

Chapter 3: SDO Channel - Cross Bus Parameter Access Mechanism

SDO (Service Data Object) channel is used for reading and writing parameter data, and is the core tool for remote configuration and diagnosis.

3.1 Dual channel design of SDO1 and SDO2

Each frequency converter provides two SDO channels (Chapter 4.7.1):

SDO1: Used for parameterized access from the master station (PLC/PC or master station frequency converter) to the slave station.

SDO2: Reserved for online parameter monitoring of visual debugging tools (such as VPlus).

The identifier of SDO1 follows CANopen's predefined connection set by default:

Rx-SDO1 (master station → slave station): 1536+Node-ID

Tx-SDO1 (slave → master): 1408+Node-ID

3.2 SDO Message Structure and Data Access

SDO adopts the Expedited SDO protocol (Chapter 4.10.1) to complete parameter transmission within one CAN frame. The core frame structure is as follows:

Control byte: 0x22 (download/write request) or 0x40 (upload/read request).

Index/Sub Index: Index=Parameter Number (PNU), Sub Index=Dataset (DS 1-4).

Data byte: 4 bytes, used to carry uint/int (valid for the lower 2 bytes) or long (valid for all 4 bytes) type data.

3.3 Cross bus parameter access (main station frequency converter as gateway)

When the EM-SYS module and the fieldbus module (such as CM-PDP, CM-232/485) are installed together in the same frequency converter, the frequency converter serves as the system bus master and can act as a protocol gateway (Chapter 4.10.2):

Through Profibus DP (PKW channel): Fill the system bus node ID into Byte 3 (Index byte) of the communication channel to read and write parameters to the node.

Through the VABus serial protocol, cross bus access is achieved by filling in the node ID (ASCII encoding) in the reserved byte of the telegram header (Byte 1 of Inquiry or Byte 2 of Select).

This mechanism allows the upper level PLC to access all nodes of the entire system bus network through the main station frequency converter without directly connecting to each frequency converter.

Chapter 4: PDO Channel and "Virtual Link" Mapping

The PDO (Process Data Object) channel is the core of the system bus for real-time data exchange. EM-SYS provides three sets of PDO channels (PDO1, PDO2, PDO3), each containing a transmit (TxPDO) and a receive (RxPDO) direction.

4.1 PDO identifier and communication mode

The default identifier follows the CANopen predefined connection set (Chapter 4.11.1):

TxPDO1：384 + Node-ID

RxPDO1：512 + Node-ID

TxPDO2：640 + Node-ID

RxPDO2：768 + Node-ID

TxPDO3：896 + Node-ID

RxPDO3：1024 + Node-ID

Each PDO channel can be configured for two working modes (Chapter 4.11.2):

Time controlled: TxPDO sends cyclically at fixed time intervals (such as TxPDO1 Time 931); After receiving the data, RxPDO immediately forwards it to the application.

SYNC controlled: TxPDO sends a unified SYNC synchronization message after receiving it; RxPDO forwards data to the application only after receiving SYNC. This mode is suitable for scenarios that require multi axis synchronous locking.

4.2 PDO timeout monitoring

To ensure communication reliability, PDO timeout monitoring can be enabled (Chapter 4.11.3):

SYNC Timeout 939: Monitor the arrival timeout of SYNC messages.

RxPDO1/2/3 Timeout 941/942/945: Monitor the data update timeout of each RxPDO channel.

Timeout will trigger faults: F2200 (SYNC timeout), F2201-F2203 (RxPDO timeout).

4.3 "Virtual Link" Mapping - Core Innovation Mechanism

Traditional CANopen uses Mapping Parameters to define the data content of PDO. EM-SYS adopts a more intuitive "Sources and Links" approach (Chapter 4.11.5).

Principle: The output data of each functional module is assigned a source number (Source No.). The input data for each functional module is specified by the source number connected through parameters. When data is transmitted across two frequency converters, a 'virtual link' is formed.

TxPDO data packaging (sender):

Each TxPDO contains 8 bytes and can flexibly package different types of data (Chapter 4.11.5.1):

4 Boolean variables (each occupying 2 bytes, actually using 1 bit) or 4 Word/Integer variables (each occupying 2 bytes) or 2 Long variables (each occupying 4 bytes), or mixed packaging.

The sender fills the required data source number into the specified byte position of TxPDO through parameters:

For example, TxPDO1 Word1 950=740 (place the control word source 740 into the 1st/2nd byte of TxPDO1).

For example, TxPDO1 Long1 954=62 (insert reference frequency source 62 into bytes 1-4 of TxPDO1).

RxPDO data unpacking (recipient):

The receiver's RxPDO maps the received 8-byte data to available source numbers (Section 4.11.5.2):

RxPDO1 byte 1/2 corresponds to source number 704 (Boolean) or 705 (Word).

RxPDO1 bytes 1-4 correspond to source number 708 (Long).

The receiver connects the RxPDO source number to the input of the target function through parameters:

For example, Control Word 99=704 (connect the Boolean source 704 of RxPDO1 to the local control word input).

For example, Reference Ramp input=708 (connect the Long source 708 of RxPDO1 to the local reference value input).

Chapter 5: System Bus Engineering Planning and Capacity Calculation

Before building the actual system, rigorous engineering planning must be carried out (Chapter 4.14).

5.1 Three Step Planning Method

Define communication relationship: Clarify which TxPDO pairs with which RxPDO (by matching identifiers) to form a data stream.

Establish virtual links: Determine which source data is packaged in each TxPDO, and which target functions are driven by each RxPDO's data.

Capacity check: Calculate the bus load rate to ensure reliable communication.

5.2 Bus load rate calculation

Each PDO frame is fixed at 8 bytes of data, plus protocol overhead, with a maximum frame length of approximately 140 bits. Bus load rate=(sum of transmission times of all TxPDOs)/unit time.

For example, at 1000 kbps, the frame transmission time of a single TxPDO is approximately 140 μ s. If sent at 1ms intervals, the load rate of this PDO is 14%.

Safety limit (Chapter 4.14.3): ≤ 80% (OK), 80-90% (critical),>90% (not feasible, may result in message loss).