CAN Physical Layer - 3

Bus Levels

CAN specifies two logical states: recessive and dominant. ISO-11898 defines a differential voltage to represent recessive and dominant states (or bits), as shown in Figure 3.

FIGURE 3: DIFFERENTIAL BUS

In the recessive state, the differential voltage on CANH and CANL is less than the minimum threshold (<0.5V receiver input or <1.5V transmitter output)(See Figure 4). In the dominant state, the differential voltage on CANH and CANL is greater than the minimum threshold. A dominant bit overdrives a recessive bit on the bus to achieve nondestructive bitwise arbitration.

FIGURE 4: ISO11898 NOMINAL BUS LEVELS