Servo CANopen Communication Protocol

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1. CANopen Network Communication

CANopen is a network transmission application layer protocol based on the CAN bus, following a master-slave communication architecture. Master and slave nodes read/write dictionary content data and exchange other information via Process Data Objects (PDO) and Service Data Objects (SDO). The CiA 301 (DS301) protocol standard defines the basic communication framework of CANopen, while CiA 402 (DS402) defines the specific implementation and standards for drives and motion control. Through this set of standard specifications, motion devices and control devices from different manufacturers can be more easily integrated and used together.

2. CIA301

2.1 Communication Identifier

CANopen defines the 11-bit CAN 2.0A ID as: COB-ID = Function code (bits 10–7) + Node address (bits 6–0).

COB-ID Composition Format

10bit ~ 7bit	6bit ~ 0bit
Function Code	NodeID

COB-ID Allocation Table

Communication Object	Function Code	Node ID	COB-ID
NTM	0000b	0	0h
SYNC	0001b	0	80h
EMCY	0001b	1 - 127	80h+NodeID
TPDO1	0011b	1 - 127	180h+NodeID
TPDO2	0101b	1 - 127	280h+NodeID
TPDO3	0111b	1 - 127	380h+NodeID
TPDO4	1001b	1 - 127	480h+NodeID
RPDO1	0100b	1 - 127	200h+NodeID
RPDO2	0110b	1 - 127	300h+NodeID
RPDO3	1000b	1 - 127	400h+NodeID
RPDO4	1010b	1 - 127	500h+NodeID
TSDO	1011b	1 - 127	580h+NodeID
RSDO	1100b	1 - 127	600h+NodeID
HeartBeat	0100b	1 - 127	700h+NodeID
boot up	0100b	1 - 127	700h+NodeID

2.2 Network Management (NMT)

NMT (Network Management System) initializes, starts, and stops network nodes. It follows a master-slave architecture and supports only a single NMT master.

The following NMT commands are defined:

NMT Command Code	Description	Allowed Communication Objects
0x01	Node state changes to operational	SDO, NMT, EMCY, Heartbeat
0x02	Node state changes to stopped	EMCY, NMT, Heartbeat
0x80	Node state changes to pre-operational	SDO、PDO、NMT、SYNC、EMECY、Heartbeat
0x81	Reset Node	Upon reset, the node enters the Initialization state
0x82	Reset Communication	Reset communication: Only communication parameters are reset. The node enters the Initialization state

The following NMT status codes are defined:

NMT Status Code	Description
0x00	Boot-up State
0x04	Stopped State
0x05	Operational State
0x7f	Pre-operational State

NMT Message

COB-ID	Bit0	Bit1
000h	NMT Command	NodeID

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Note: Node ID = 1–127. 0 = broadcast command.

2.3 Service Data Object (SDO)

SDO is mainly used for parameter configuration of slave nodes by the CANopen master. Service confirmation is the most significant feature of SDO, generating an acknowledgment for each message to ensure data transmission accuracy. In a CANopen system, typically the CANopen slave node acts as the SDO server, and the CANopen master node acts as the client (referred to as CS communication). The SDO client can access the object dictionary on the SDO server via index and subindex. This allows the CANopen master to access parameters of any object dictionary entry on the slave node. Additionally, SDO can transmit data of any length (when the data length exceeds 4 bytes, it is split into multiple messages for transmission).

SDO Write Operation Format

Operation	COB-ID	Bit0	Bit1&Bit2	Bit3	Bit4~Bit7
Send	600h+NodeID	23h	Index	Subindex	Data (4 bytes)
Send	600h+NodeID	27h	Index	Subindex	Data (3 bytes)
Send	600h+NodeID	2Bh	Index	Subindex	Data (2 bytes)
Send	600h+NodeID	2Fh	Index	Subindex	Data (1 bytes)
return	580h+NodeID	60h	Index	Subindex	Zero Padding
return	580h+NodeID	80h	Index	Subindex	Abort Code

SDO Read Operation Format

Operation	COB-ID	Bit0	Bit1&Bit2	Bit3	Bit4~Bit7
Send	600h+NodeID	40h	Index	Subindex	Zero Padding
return	580h+NodeID	43h	Index	Subindex	Data (4 bytes)
return	580h+NodeID	47h	Index	Subindex	Data (3 bytes)
return	580h+NodeID	4Bh	Index	Subindex	Data (2 bytes)
return	580h+NodeID	4Fh	Index	Subindex	Data (1 bytes)
return	580h+NodeID	80h	Index	Subindex	Abort Code

SDO Abort Code

Abort Code	Description
05 04 00 01	Invalid or unknown SDO command specifier
06 01 00 01	Attempt to read a write-only object
06 01 00 02	Attempt to write a read-only object
06 02 00 00	Object does not exist in the object dictionary
06 04 00 41	Object cannot be mapped to PDO
06 07 00 12	Data type mismatch
06 09 00 11	Subindex does not exist
06 09 00 30	Parameter value out of range
08 00 00 24	No data available

2.4 Process Data Object (PDO)

PDO belongs to process data and is used for unidirectional transmission of real-time data. It does not require acknowledgment CAN messages from receiving nodes to confirm reception, following the producer-consumer model. From the perspective of a slave node, PDOs can be divided into RPDO and TPDO. The final transmission method is determined by both the communication parameters and the mapping parameters.

RPDO/TPDO mapping object address definition:

Bit31~Bit16	Bit15~Bit8	Bit7~Bit0
Index	Subindex	Bit Length

PDO object list:

Name	COB-ID	Communication Object	Mapped Object
RPDO1	200h+NodeID	1400h	1600h
RPDO2	300h+NodeID	1401h	1601h
RPDO3	400h+NodeID	1402h	1602h
RPDO4	500h+NodeID	1403h	1603h
TPDO1	180h+NodeID	1800h	1A00h
TPDO2	280h+NodeID	1801h	1A01h
TPDO3	380h+NodeID	1802h	1A02h
TPDO4	480h+NodeID	1803h	1A03h

PDO Communication Parameters: The COB-ID, status bits, transmission type, inhibit time, and event timer related to the PDO can all be configured through the corresponding communication object dictionary.

PDO Mapping Parameters: The actual data content of the PDO can be set by configuring the mapping object dictionary corresponding to the PDO.

2.5 Sync Object (SYNC)

SYNC object: A mechanism for synchronizing transmission/reception among multiple nodes. Mainly used for synchronous PDO transmission. Configurable via object dictionary: 1005h (SYNC COB-ID), 1006h (Cycle Period), 1007h (Sync Window Length).

COB-ID	Data
80h	None

2.6 Emergency Object (EMCY)

EMCY: Triggered by internal device errors. Sends error code to NMT master. Diagnostic message, does not affect communication. CAN-ID: stored at index 1014h, typically 080h + NodeID. Data length: 8 bytes.

Upon node fault, update the error register and pre-defined error field. Emergency message content shall adhere to the following specifications:

COB-ID	Bit0&Bit1	Bit2	Bit3	Bit4~Bit7
80h+NodeID	Error Code	Error Register	Reserved	Auxiliary bytes

Error Code:Error code Latest value in pre-defined error field (1003h). See object dictionary for details.

Error Register:Error register Value in error register (1001h). See object dictionary for details.

Auxiliary bytes:Auxiliary bytes Manufacturer-specific values.

2.7 Special Message

2.7.1 Boot-up Message

First power-on message

COB-ID	Bit0
700h+NodeID	00h

2.7.2 Heartbeat Message

Parameter/Cycle Setting: The heartbeat period (in milliseconds) is configured via object dictionary index 0x1017. A value of 0 disables the heartbeat function.

Timeout Mechanism: The master node defines a timeout threshold for each slave node. If a heartbeat is not received before the timeout expires, the slave node is considered offline, and an error is triggered.

COB-ID	Bit0
700h+NodeID	Operational State

3 CIA402

3.1 State Machine

3.2 Control Word

BIT	Content	Description	Note
0	so	Switch on	1 = valid
1	ev	Enable voltage	Fixed to 1
2	qs	quick stop	0 = valid
3	eo	Enable operation	1 = valid
4~6	oms	Operation mode specific	-
7	fr	Fault reset	1 = valid
8	h	Halt	-
9	h	Operation mode specific	-
10	r	Reserved	-
11~15	r	Manufacturer-Specific	-

3.3 Status Word

BIT	Name	Description	Note
0	rtso	Ready	Fixed to 1
1	so	Start	Fixed to 1
2	oe	Enable operation	1 = valid
3	f	Fault	1 = valid
4	ve	Enable voltage	Fixed to 1
5	qs	Quick stop	0 = valid
6	sod	swd	Fixed to 1
7	w	Warning	1 = valid
8	ms	Manufacturer-specific	-
9	rm	Remote	Fixed to 1
10	tr	Target reached	-
11	ite	Limit	-
12~13	oms	Special definition	-
14~15	ms	Manufacturer-specific	-

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Servo CANopen Communication Protocol
1. CANopen Network Communication
2. CIA301
2.1 Communication Identifier
2.2 Network Management (NMT)
2.3 Service Data Object (SDO)
2.4 Process Data Object (PDO)
2.5 Sync Object (SYNC)
2.6 Emergency Object (EMCY)
2.7 Special Message
2.7.1 Boot-up Message
2.7.2 Heartbeat Message
3 CIA402
3.1 State Machine
3.2 Control Word
3.3 Status Word