Preface
MPC5565 Microcontroller Reference Manual, Rev. 1.0
21-14
Freescale Semiconductor
21.3.3.3
Free Running Timer (CAN
x
_TIMER)
CAN
x
_TIMER represents a 16-bit free running counter that can be read and written by the CPU. The timer
starts from 0x0000 after Reset, counts linearly to 0xFFFF, and wraps around.
The timer is clocked by the FlexCAN2 bit-clock (which defines the baud rate on the CAN bus). During a
message transmission/reception, it increments by one for each bit that is received or transmitted. When
there is no message on the bus, it counts using the previously programmed baud rate. During freeze mode,
the timer is not incremented.
The timer value is captured at the beginning of the identifier field of any frame on the CAN bus. This
captured value is written into the TIME STAMP entry in a message buffer after a successful reception or
transmission of a message.
25
BOFFREC
Bus off recovery mode. Defines how FlexCAN2 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 FlexCAN2 will re-synchronize 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.
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. 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 FlexCAN2 stations with
a special SYNC message (that is, global network time).
0 Timer sync feature disabled
1 Timer sync feature enabled
Note:
There is a possibility of 4
–
5 ticks count skew between the different FlexCAN2 stations that would
operate in this mode.
27
LBUF
Lowest buffer transmitted first. This bit defines the ordering mechanism for message buffer transmission.
0 Buffer with lowest ID is transmitted first
1 Lowest number buffer is transmitted first
28
LOM
Listen-only mode. Configures FlexCAN2 to operate in listen-only mode. In this mode, the FlexCAN2 module
receives messages without giving any acknowledge. It is not possible to transmit any message in this mode.
0 FlexCAN2 module is in normal active operation, listen only mode is deactivated
1 FlexCAN2 module is in listen only mode operation
29–31
PROPSEG
[0:2]
Propagation segment. Defines the length of the propagation segment in the bit time. The valid
programmable values are 0
–
7.
1
One time quantum is equal to the S clock period.
Table 21-8. CAN
x
_CR Field Descriptions
Bits
Description
Propagation Segment Time
(P 1)
Time Quanta
×
=
Time Quantum = one S clock period
Содержание MPC5565
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