XC886/888CLM
Controller Area Network (MultiCAN) Controller
User’s Manual
15-9
V1.3, 2010-02
MultiCAN, V1.0
quanta is requested by the ISO standard. According to ISO standard, a CAN bit time,
calculated as the sum of T
Sync
, T
Seg1
and T
Seg2
, must not fall below 8 time quanta.
Calculation of the bit time:
To compensate phase shifts between clocks of different CAN controllers, the CAN
controller must synchronize on any edge from the recessive to the dominant bus level.
If the hard synchronization is enabled (at the start of frame), the bit time is restarted at
the synchronization segment. Otherwise, the re-synchronization jump width T
SJW
defines
the maximum number of time quanta, a bit time may be shortened or lengthened by one
re-synchronization. The value of SJW is defined by bit field NBTRx.SJW.
The maximum relative tolerance for
f
CAN
depends on the Phase Buffer Segments and
the re-synchronization jump width.
A valid CAN bit timing must be written to the register NBTR before resetting the bit NCRx.
INIT, i.e., before enabling the operation of the CAN node. The register NBTRx may be
written only if bit NCRx.CCE (Configuration Change Enable) is set.
15.1.3.2
Bitstream Processor
Based on the message objects in the message buffer, the Bit Stream Processor
generates the remote and data frames to be transmitted via the CAN bus. It controls the
CRC generator and adds the checksum information to the new remote or data frame.
After including the ‘Start of Frame Bit’ and the ‘End of Frame Field’, the Bit Stream
t
q
= (BRP + 1) /
f
CAN
if DIV8 = 0
= 8
×
(BRP+1) /
f
CAN
if DIV8 = 1
T
Sync
= 1
×
t
q
T
Seg1
= (TSEG1 + 1)
×
t
q
(min. 3
t
q
)
T
Seg2
= (TSEG2 + 1)
×
t
q
(min. 2
t
q
)
bit time = T
Sync
+ T
Seg1
+ T
Seg2
(min. 8
t
q
)
T
SJW
= (SJW + 1)
×
t
q
T
Seg1
≥
T
SJW
+ T
prop
T
Seg2
≥
T
SJW
d
f
CAN
≤
min (T
b1
, T
b2
) / 2
×
(13
×
bit time - T
b2
)
AND
d
f
CAN
≤
T
SJW
/ 20
×
bit time
*
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