Dominant / Recessive

A basic prerequisite for smooth communication in a CAN network — especially for bus access, fault indication and acknowledgement — is clear distinctions between dominant and recessive bus levels. The dominant bus level corresponds to logical “0”. The recessive bus level corresponds to logical “1”.

The dominant bus level overwrites the recessive bus level. When different CAN nodes send dominant and recessive bus levels simultaneously, the CAN bus assumes the dominant bus level. The recessive bus level only occurs if all CAN nodes send recessive levels.

AND-logic

In terms of logic, such behavior is AND-logic. Physically, AND-logic is implemented by a so-called open collector circuit. Practice with the interactive figure “Bus Logic” to learn about the wired-AND bus logic upon which a CAN network is based.