10.4.1 CAN Bus States

The CAN bus has two logical states during operation: recessive and dominant. See Figure 31 and Figure 32.

Recessive bus state is when the high resistive internal input resistors of each node's receiver bias the bus to a common mode of about 1.85 V across the bus termination resistors. Recessive is equivalent to logic high and is typically a differential voltage on the bus of about 0 V. Recessive state is also the idle state.

Dominant bus state is when the bus is driven differentially by one or more drivers. Current is induced to flow through the termination resistors and generate a differential voltage on the bus. Dominant is equivalent to logic low and is a differential voltage on the bus greater than the minimum threshold for a CAN dominant. A dominant state overwrites the recessive state.

During arbitration, multiple CAN nodes may transmit a dominant bit at the same time. In this case the differential voltage of the bus will be greater than the differential voltage of a single driver.

The host microprocessor of the CAN node will use the TXD terminal to drive the bus and will receive data from the bus on the RXD pin.

Transceivers with low power Standby Mode have a third bus state where the bus terminals are weakly biased to ground via the high resistance internal resistors of the receiver. See Figure 31 and Figure 32.

Figure 31. Bus States (Physical Bit Representation)

A. Normal and Silent Modes B. Standby and Shutdown Modes Figure 32. Simplified Recessive Common Mode Bias Unit and Receiver

The devices have four main operating modes:

1. Normal mode (all devices)
2. Silent mode (TCAN330, TCAN337)
3. Standby mode with wake (TCAN334)
4. Shutdown mode (TCAN330, TCAN334)