SWRU626 December 2025 CC3501E , CC3551E
The DCAN is set in Bus Monitoring Mode by programming CCCR.MON to one. In Bus Monitoring Mode (see ISO 11898-1:2015, 10.14 Bus monitoring), the DCAN is able to receive valid data frames and valid remote frames, but cannot start a transmission. In this mode, it sends only recessive bits on the CAN bus. If the DCAN is required to send a dominant bit (ACK bit, overload flag, active error flag), the bit is rerouted internally so that the DCAN monitors this dominant bit, although the CAN bus may remain in recessive state. In Bus Monitoring Mode register TXBRP is held in reset state.
The Bus Monitoring Mode can be used to analyze the traffic on a CAN bus without affecting it by the transmission of dominant bits. Figure 25-2 shows the connection of signals d_can_tx and d_can_rx to the DCAN in Bus Monitoring Mode.