NXP Semiconductors MPC5777C - Page 93

Restricted Operation Mode is automatically entered when the Tx Handler was not able to
read data from the Message RAM in time. To leave Restricted Operation Mode, the Host
CPU has to reset CCCR[ASM].
The Restricted Operation Mode can be used in applications that adapt themselves to
different CAN bit rates. In this case the application tests different bit rates and leaves the
Restricted Operation Mode after it has received a valid frame.
NOTE
The Restricted Operation Mode must not be combined with the
Loop Back Mode (internal or external).
3.5.1.6 Bus Monitoring Mode
The M_CAN is set in Bus Monitoring Mode by programming CCCR.MON to one. In
Bus Monitoring Mode (see ISO11898-1, 10.12 Bus monitoring), the M_CAN 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 M_CAN is required to send a
dominant bit (ACK bit, overload flag, active error flag), the bit is rerouted internally so
that the M_CAN 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 The following figure shows the
connection of signals M_CAN Tx and Rx to the M_CAN in Bus Monitoring Mode.
=1
MCAN
transmit output
MCAN
receive input
MCAN
TX
RX
Figure 3-50. Pin Control in Bus Monitoring Mode
Chapter 3 Modular CAN (M_CAN)
MPC5777C Reference Manual Addendum, Rev. 1, 12/2015
Freescale Semiconductor, Inc. 93