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FlexCAN Module
MPC5644A Microcontroller Reference Manual, Rev. 6
1410
Freescale Semiconductor
SMP
Sampling Mode
This bit defines the sampling mode of CAN bits at the Rx input.
1: Three samples are used to determine the value of the received bit: the regular one (sample
point) and 2 preceding samples, a majority rule is used
0: Just one sample is used to determine the bit value
BOFFREC
Bus Off Recovery Mode
This bit defines how FlexCAN recovers from Bus Off state. If this bit is negated, automatic
recovering from Bus Off state occurs according to the CAN Specification 2.0B. If the bit is asserted,
automatic recovering from Bus Off is disabled and the module remains in Bus Off state until the
bit is negated by the user. If the negation occurs before 128 sequences of 11 recessive bits are
detected on the CAN bus, then Bus Off recovery happens as if the BOFFREC bit had never been
asserted. If the negation occurs after 128 sequences of 11 recessive bits occurred, then FlexCAN
will resynchronize to the bus by waiting for 11 recessive bits before joining the bus. After negation,
the BOFFREC bit can be re-asserted again during Bus Off, but it will only be effective the next time
the module enters Bus Off. If BOFFREC was negated when the module entered Bus Off, asserting
it during Bus Off will not be effective for the current Bus Off recovery.
1: Automatic recovering from Bus Off state disabled
0: Automatic recovering from Bus Off state enabled, according to CAN Spec 2.0 part B
TSYN
Timer Sync Mode
This bit enables a mechanism that resets the free-running timer each time a message is received
in Message Buffer 0. This feature provides means to synchronize multiple FlexCAN stations with
a special “SYNC” message (i.e., global network time). If the FEN bit in MCR is set (FIFO enabled),
MB8 is used for timer synchronization instead of MB0.
1: Timer Sync feature enabled
0: Timer Sync feature disabled
LBUF
Lowest Buffer Transmitted First
This bit defines the ordering mechanism for Message Buffer transmission. When asserted,
MCR[LPRIO_EN] does not affect the priority arbitration.
1: Lowest number buffer is transmitted first
0: Buffer with highest priority is transmitted first
LOM
Listen-Only Mode
This bit configures FlexCAN to operate in Listen Only Mode. In this mode, transmission is
disabled, all error counters are frozen and the module operates in a CAN Error Passive mode.
Only messages acknowledged by another CAN station will be received. If FlexCAN detects a
message that has not been acknowledged, it will flag a BIT0 error (without changing the REC), as
if it was trying to acknowledge the message.
1: FlexCAN module operates in Listen Only Mode
0: Listen Only Mode is deactivated
PROPSEG
Propagation Segment
This 3-bit field defines the length of the Propagation Segment in the bit time. The valid
programmable values are 0
–
7.
Propagation Segment Time = (P 1) * Time-Quanta.
Time-Quantum = one Sclock period.
Table 32-10. CR Register field descriptions
Field
Description
Summary of Contents for MPC5644A
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