Nuvoton ARM Cortex NuMicro M451 Series, Техническое справочное руководство

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M451
May. 4, 2018 Page 872 of 1006 Rev.2.08
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Sync_Seg Prop_Seg Phase_Seg1 Phase_Seg2
Normal CAN Bit Time
1 Time Quantum(
t
q
)
Sample Point
Figure 6.20-7 Bit Timing
Parameter Range Remark
BRP [1..32] Defines the length of the time quantum t
q
Sync_Seg
1 t
q
Fixed length, synchronization of bus input to APB clock
Prop_Seg [1..8] t
q
Compensates for the physical delay time
Phase_Seg1 [1..8] t
q
Which may be lengthened temporarily by synchronization
Phase_Seg2
[1..8] t
q
Which may be shortened temporarily by synchronization
SJW [1..4] t
q
Which may not be longer than either Phase Buffer Segment
This table describes the minimum programmable ranges required by the CAN protocol
Table 6-38 CAN Bit Time Parameters
A given bit rate may be met by different bit time configurations, but for the proper function of the CAN
network the physical delay time and the oscillator’s tolerance range have to be considered.
Propagation Time Segment 6.20.7.17
This part of the bit time is used to compensate physical delay time within the network. These delay
time consist of the signal propagation time on the bus and the internal delay time of the CAN nodes.
Any CAN node synchronized to the bit stream on the CAN bus will be out of phase with the transmitter
of that bit stream, caused by the
signal propagation time between the two nodes. The CAN protocol’s
non-destructive bitwise arbitration and the dominant acknowledge bit provided by receivers of CAN
messages requires that a CAN node transmitting a bit stream must also be able to receive dominant
bits transmitted by other CAN nodes that are synchronized to that bit stream. The example in the
Figure 6.20-8 shows the phase shift and propagation time between two CAN nodes.