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NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 790 -
Revision V1.30
NUC97
0
T
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CHNIC
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enough; the dominant spike is sampled as actual bus level.
Rx-Input
recessive
dominant
Sync_Seg
Prop_Seg
Phase_Seg
Prop_Seg
Sample-Point
Sample-Point
Spike
SJW >= Phase Error
Rx-Input
recessive
dominant
Sample-Point
Sample-Point
Spike
SJW < Phase Error
Figure 5.24-10 Filtering of Short Dominant Spikes
Oscillator Tolerance Range
5.24.7.19
The oscillator tolerance range was increased when the CAN protocol was developed from version 1.1
to version 1.2 (version 1.0 was never implemented in silicon). The option to synchronize on edges
from dominant to recessive became obsolete, only edges from recessive to dominant are considered
for synchronization. The protocol update to version 2.0 (A and B) had no influence on the oscillator
tolerance.
The tolerance range d
f
for an oscillator frequency f
osc
around the nominal frequency f
nom
is:
(1
–
df)
.
fnom <= fosc <= (1 + df)
.
fnom
It depends on the proportions of Phase_Seg1, Phase_Seg2, SJW, and the bit time. The maximum
tolerance df is the defined by two conditions (both shall be met):
min (Phase_Seg1, Phase_Seg2)
I: df <= -------------------------------------------------
2 * (13* bit_time
– Phase_Seg2)
SJW
II: df <= -----------------
20 * bit_time
Note:
These conditions base on the APB cock = f osc.
It has to be considered that SJW may not be larger than the smaller of the Phase Buffer Segments