CAN dictionary

Explains vocabulary and abbreviations used in CAN technology

Alphabetic selection:



The bandwidth is the value which denominates the size of information transmitted in a defined time unit.

base frame format

The base frame format uses 11-bit identifiers in Classical CAN data and CAN remote frames (CBFF) as well as in CAN FD data frames (FBFF).

basic cycle

The base frame format uses 11-bit identifiers in Classical CAN data and CAN remote frames (CBFF) as well as in CAN FD data frames (FBFF).


A term used in the early days of CAN describing an implementation which uses just two receive message buffers filled and read out in a ping pong method.

bit encoding

In TTCAN the basic cycle always starts with the reference message followed by a number of exclusive, arbitration or free windows. One or more basic cycles make the TTCAN matrix cycle.

bit error

If a bit is transmitted as dominant and received as recessive or vice versa, this is regarded as a bit error condition that causes an error frame transmission in the next bit time. If a recessive transmitted bit is overwritten by a dominant one in arbitration field and acknowledge slot, this is not a bit error.

bit monitoring

All transmitting CAN controller chips listen to the bus and monitor the bits that are transmitted by them.

bit rate

Number of bits per time during trans­ mission, independent of bit representation. The bit rate in Classical CAN is limited to 1 Mbit/s. In the CAN FD protocol, the bit rate may be higher in the data phase. In the arbitration phase, the bit rate is still limited to 1 Mbit/s.

bit rate switch (BRS)

At the sample point of the bit rate switch (BRS) bit in CAN FD data frames, the data phase starts. This means that here the CAN controllers may switch to a higher bit rate. The BRS bit exists in CAN FD data frames only.

bit resynchro­nization

Due to local oscillator tolerances it may happen that one node loses the bit synchronization. Each recessive-to­ dominant edge causes the CAN controller to resynchronize itself to the received falling edge.

bit stuffing

Injections of bits into a bit stream to provide bus state changes required for periodic resynchronization when using an NRZ bit representation.

bit time

Duration of one bit.

bit timing

The setting of the bit timing registers in the CAN controller chip is based on the time quantum, which derives from the oscillator frequency and the node-specific bit rate pre-scaler.

boot-up message

CANopen communication service transmitted whenever a node enters the NMT pre-operational state after initialization.


A device that provides data link layer communication between two networks.

broadcast transmission

A communication service performing a simultaneous transmission from one to all nodes.


See bit rate switch.


Topology of a communication network, where all nodes are reached by passive links. This allows transmission in both directions.

bus access

When the bus is idle, any node may start to transmit a frame. In CAN networks the nodes access the bus by transmitting the dominant SOF (start of frame) bit.

bus analyzer

Tool which monitors the bus and dis­plays the transmitted bits. Bus analyzers are available for the physical layer, the data link layer, and different application layers (e.g. CANopen or DeviceNet).

bus arbitration

If at the very same moment several nodes try to access the bus, an arbitration process is necessary to control which node may transmit while the other nodes have to delay their transmission. The bus arbitration process used in CAN protocol is CMSA/CD (Carrier Sense Multiple Access/Collision Detection) with AMP (Arbitration on Message Priority). This allows bus arbitration without destruction of messages.

bus comparator

Electronic circuitry that converts physical signals used for transfer across the communication medium back into logical information or data signals.

bus driver

Electronic circuitry that converts logical information or data signals into physical signals so that these signals can be transferred across the communication medium.

bus idle

During bus idle state no CAN frame is transmitted and all connected nodes transmit recessive bits.

bus latency

The time between the transmission request and the transmission of the SOF (start of frame) bit. In CAN networks this may be in maximum one message duration minus one bit time.

bus length

The network cable length between the two termination resistors. The bus length of CAN networks is limited by the used transmission rate. At 1 Mbit/s the maximum length is theoretically 40 m. When using lower transmission rates, longer bus lines may be used: at 50 kbit/s a length of 1 km is possible.

bus monitoring mode

In this mode, the CAN controller has switched off the Tx pin. This means no error flag or no ACK slot can be transmitted.

bus off state

The CAN controllers switch to bus­ off state when the TEC (transmit error counter) has reached 256. During bus­ off state, the CAN controller transmits recessive bits.

bus on

A CAN controller is said to be “on the bus” or “bus on” if it’s actively participating in the bus traffic.

bus state

Either of the two complementary logical states: dominant (logical 0) or recessive (logical 1).


The busload is the ratio of transmitted bits to bus idle bits within a defined time unit. 100% means that bits are transmitted during the complete defined time unit and 0% means that the bus is in bus idle state during the complete defined time unit.

Source CANdictionary (2016) - CiA CAN in Automation -