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BOSCH
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Revision 1.6TTCAN
11.11.02
manual_about.fm
If more than one configuration is possible, that configuration allowing the highest oscillator
tolerance range should be chosen.
CAN nodes with different system clocks require different configurations to come to the same
bit rate. The calculation of the propagation time in the CAN network, based on the nodes with
the longest delay times, is done once for the whole network.
The CAN system’s oscillator tolerance range is limited by that node with the lowest tolerance
range.
The calculation may show that bus length or bit rate have to be decreased or that the oscillator
frequencies’ stability has to be increased in order to find a protocol compliant configuration of
the CAN bit timing.
The resulting configuration is written into the Bit Timing Register:
(Phase_Seg2-1)&(Phase_Seg1+Prop_Seg-1)&(SynchronisationJumpWidth-1)&(Prescaler-1)
4.2.1.7 Example for Bit Timing at high Baudrate
In this example, the frequency of CAN_CLK is 10 MHz, BRP is 0, the bit rate is 1 MBit/s.
t
q
100 ns = t
CAN_CLK
delay of bus driver 50 ns
delay of receiver circuit 30 ns
delay of bus line (40m) 220 ns
t
Prop
600 ns = 6 • t
q
t
SJW
100 ns = 1 • t
q
t
TSeg1
700 ns = t
Prop
+ t
SJW
t
TSeg2
200 ns = Information Processing Time + 1 • t
q
t
Sync-Seg
100 ns = 1 • t
q
bit time 1000 ns = t
Sync-Seg
+ t
TSeg1
+ t
TSeg2
tolerance for CAN_CLK 0.39 % =
=
In this example, the concatenated bit time parameters are (2-1)
3
&(7-1)
4
&(1-1)
2
&(1-1)
6
, the Bit
Timing Register is programmed to= 0x1600.
min PB
1
PB
2,()
2 13 bit time PB2–×()×
----------------------------------------------------------------
0.1µ
s
2131µ
s
0.2µ
s
–×()×
-----------------------------------------------------------