CAN dictionary

Explains vocabulary and abbreviations used in CAN technology

Alphabetic selection:


safe-guard cycle time (SCT)

Defines the maximum time between two periodically transmitted SRDOs (see EN 50325-5).

SafetyBus p

This CAN-based higher-layer protocol and implementation specification by the Safety Network International e. V. is de­ dicated for safety-related communication within factory automation. It meets the safety integrity level (SIL) 3 according to IEC 61508.

safety-related logical device (SRLD)

A CANopen device participating in the safe communication as specified in EN 50325-5.

safety-related object validation time (SRVT)

Defines the maximum time between the two CAN messages that make an SRDO (see EN 50325-5).

safety-relevant data object (SRDO)

SRDO as defined in the CANopen safety protocol (EN 50325-5) is made of two CAN messages. The second message contains in the data field the bit-wise converted data of the first message.

sample point

The sample point is the point of time at which the bus level is read and interpreted as the value of the respective bit. Its location is between Phase_Seg 1 and Phase_Seg 2.


See safe-guard cycle time.


See service data object.

SDO block transfer

SDO block transfer is a CANopen communication service for increasing the speed of uploading/downloading data to/from a CANopen device. It is defined in CiA 301 v. 4.2.0. In SDO block transfer, the confirmation is sent after the reception of a number of SDO segments.

SDO manager

In CANopen, the SDO manager handles the dynamic establishment of SDO connections. It resides on the very same node as the NMT master functionality.

secondary sample point (SSP)

The SSP is located after the (first) sample point and is set to a fix value or a value derived from the actual transmitter delay. If transmitter delay compensation is applied, the bus state sampled at the SSP is valid.

segmented SDO

If objects longer than 4 byte are transmitted by means of SDO services (see 301 v. 4.2.0 and former). a segmented transfer is used. The data is transmitted in segments of up to 7 byte of application data. The number of segments is theoretically not limited.

server SDO

The server SDO receives the SDO messages from the corresponding client and responses each SDO message (expedited and segmented SDO transfer or a block of SDO messages (SDO block transfer).

service data object (SDO)

The SDO is a confirmed communication service that provides access to all entries in the CANopen object dictionary. An SDO uses two 8-byte CAN messages with different identifiers. The SDO may transmit segmented any amount of data. Each segment (segmented SDO) or a number of segments (SDO block transfer) is confirmed.

SI unit

International system of units for physical values as specified in ISO 80000-1:2013.

single-shot transmission

Some CAN controllers provide a single-shot mode, which means that the message will not be retransmitted automatically when an error has been detected. This mode is required for TTCAN.

single-wire CAN (SWC)

Physical layer using only one bus line and CAN ground. The SAE specified a SWC transceiver in J2411.

sleep mode

CAN controller and transceiver may be operated in stand-by or low-power (sleep) mode not more driving the bus lines.

SOD network indication

This function is used to address a remote CANopen device in another (not directly accessible) CANopen network. This service and protocol establishes a virtual channel in order to perform any SDO communication. The SDO services are defined in CiA 301 v. 4.2.0 and former versions.


See start of frame.

source address mode (SAM)

In the SAM mode of a CANopen MPDO, a multiplexer (16-bit index and 8-bit sub­ index of an object) refers to the MPDO producer. The MPDO producer may use a scanner list (objects to be sent). The MPDO consumers may use a dispatcher list showing which source multiplexer references to which destination multiplexer.


See safety-relevant data object.


See safety-related logical device.


See substitute remote request.


See safety-related object validation time.

standard CAN

Also called CAN 2.0A – the original protocol variant where the identifiers are 11 bit long. Also see Extended CAN.

star topology

In some passenger cars, CAN networks are installed in a star topology terminating the network in the center of the star.

start of frame (SOF)

The very first bit of any data and remote frames (only in Classical CAN). The SOF state is always dominant.

stopped state

Part of the CAN open NMT slave state machine (FSA). In this NMT state only NMT messages are performed and under certain conditions error control messages are transmitted.

stuff count

In CAN FO frames, the stuff count is at the beginning of the CRC field. It consists of the stuff-bit count modulo 8 in a three­ bit Gray code followed by a parity bit.

stuff error

In CAN FD frames, the stuff count is at the beginning of the CRC field. It consists of the stuff-bit count modulo 8 in a three­ bit Gray code followed by a parity bit.


Whenever a CAN transmitter detects 5 consecutive bits of identical value in the bit stream, it automatically inserts a complementary stuff-bit. The CAN receiver excludes the stuff­ bits automatically, so that the original message to be transmitted is the very same as the received message. It is used for automatic re-synchronization in the CAN module's bit timing circuitry.


8-bit sub-address to access the sub­ objects of arrays and records in a CANopen object dictionary.

substitute remote request (SRR)

This bit is transmitted only in CEFF and in FEFF after ID-bit 18, at the position of the RTR bit in CBFF or of the RRS bit in FBFF. The SRR is transmitted recessively, but receivers accept recessive and dominant SRR bits.

suspend transmission

CAN controllers in error passive mode have to wait additional 8 bit times before the next data or remote frame (only in Classical CAN) may be transmitted.


See single-wire CAN.

SYNC counter

The optional parameter SYNC counter is used in CANopen networks to define an explicit relationship between the current SYNC cycle and PDO transmission.

SYNC data frame

The CAN data frame containing one part of the current value of a time-base as defined in CiA 603 (in development).

SYNC message

Dedicated CANopen message forcing the receiving nodes to sample the inputs mapped into synchronous TPDOs. Receiving this message causes the node to set the outputs to values received in the previous synchronous RPDO.

sync segment (Sync_Seg)

Part of the bit time used to synchronize various nodes on the bus. An edge is expected within this segment.

system clock

Time base to coordinate the state machines in CAN implementations.

system variable

Application parameter that represents undefined shared process data of field devices with multiple CANopen devices.

Source CANdictionary (2016) - CiA CAN in Automation -