PXR40RM Datasheet, PDF (830/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

FlexCAN Module
Table 24-10. FLEXCAN_x_CTRL Field Descriptions (continued)
Field
Description
25 Bus Off Recovery Mode
BOFF_RE This bit defines how FlexCAN recovers from Bus Off state. If this bit is negated, automatic recovering from Bus Off
C
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
BOFF_REC bit had never been asserted. If the negation occurs after 128 sequences of 11 recessive bits occurred,
then FlexCAN will re-synchronize to the bus by waiting for 11 recessive bits before joining the bus. After negation,
the BOFF_REC bit can be re-asserted again during Bus Off, but it will only be effective the next time the module
enters Bus Off. If BOFF_REC was negated when the module entered Bus Off, asserting it during Bus Off will not
be effective for the current Bus Off recovery.
0 Automatic recovering from Bus Off state enabled, according to CAN Spec 2.0 part B
1 Automatic recovering from Bus Off state disabled
26
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 FLEXCAN_x_MCR is set (FIFO enabled), MB8 is used for timer
synchronization instead of MB0.
0 Timer Sync feature disabled
1 Timer Sync feature enabled
27
LBUF
Lowest Buffer Transmitted First
This bit defines the ordering mechanism for Message Buffer transmission. When asserted, the LPRIO_EN bit does
not affect the priority arbitration.
0 Buffer with highest priority is transmitted first
1 Lowest number buffer is transmitted first
28
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 [Ref. 1]. 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.
0 Listen Only Mode is deactivated
1 FlexCAN module operates in Listen Only Mode
29–31 Propagation Segment
PROPSEG 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 = (PROPSEG + 1) * Time-Quanta.
Time-Quantum = one Sclock period.
NOTES:
1 _{One time quantum is equal to the Sclock period.}
24-20
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor