FlexCAN
Freescale Semiconductor
30-10
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
30.3.3
FlexCAN Free Running Timer Register (TIMER)
This register represents a 16-bit free running counter that can be read and written to by the CPU. The timer
starts from 0x0000 after reset, counts linearly to 0xFFFF, and wraps around.
The timer is clocked by the FlexCAN bit-clock (which defines the baud rate on the CAN bus). During a
message transmission/reception, it increments by one for each received or transmitted bit. 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 (ID) field of any frame on the CAN bus. This
captured value is written into the TIMESTAMP entry in a message buffer after a successful reception or
transmission of a message.
Writing to the timer is an indirect operation. The data is first written to an auxiliary register, then an internal
request/acknowledge procedure across clock domains is executed. All this is transparent to the user, except
for the fact that the data takes some time to be actually written to the register. If desired, software can poll
the register to discover when the data was actually written.
3
LOM
Listen-only mode. 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 is received. If FlexCAN detects a message that has not been acknowledged, it flags a BIT0
error (without changing the REC), as if it was trying to acknowledge the message.
0 FlexCAN module is in normal active operation; listen-only mode is deactivated
1 FlexCAN module is in listen-only mode operation
2–0
PROPSEG
Propagation segment. Defines the length of the propagation segment in the bit time. The valid programmable
values are 0–7.
Eqn. 30-5
Note: A time-quantum equals 1 S clock period.
IPSBAR
Offset:
0x1C_0008 (TIMER)
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
TIMER
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Figure 30-6. FlexCAN Timer Register (TIMER)
Table 30-3. CANCTRL Field Descriptions (continued)
Field
Description
Propagation segment time
(P 1)
time-quanta
=
Because
of
an
order
from
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United
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International
Trade
Commission,
BGA-packaged
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part
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indicated
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prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
