Bus rate timing example, Additional bit timing examples – Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement User Manual
Page 164
High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
164
Bus Rate Timing Example
The following table shows a few example bit timing settings for common oscillator frequency and baud-rate selections. Because of the
large number of variables, there are many combinations not shown that can achieve a desired baud rate. There are a number of
approaches to determining all the bit timing factors, but this uses the most common (i.e., the oscillator frequency and baud rate have
already been determined by system constraints.)
Additional Bit Timing Examples
The following is an explanation of how the table row illustrating an oscillator frequency of 16MHz and a CAN baud rate of 125kbps is
derived.
Various combinations of BRPV are selected until one is located that meets the t
QU
per bit criteria, i.e., an integer value less than 25.
Selecting BRPV = 4, the previously described equations state that there should be 16 t
QU
per bit. That leaves 16 – 1 or 15 t
QU
remain-
ing for TS1_LEN and TS2_LEN, which are arbitrarily assigned as shown. Because BRPV > 3, the triple sampling feature (SMP = 1) can
be used, if desired.
FOSC
CCD
BRPV
TQU
BAUD
RATE
T
QU
PER BIT
TS1_LEN
TS2_LEN
SJW
SMP = 1
PERMITTED?
2
2
100ns
1Mbps
10
5
4
3
NO
2
4
200ns
500kbps
10
5
4
3
YES
2
5
250ns
250kbps
16
10
5
4
YES
40MHz
2
10
500ns
125kbps
16
10
5
4
YES
0.5
2
125ns
1Mbps
16
10
5
4
NO
1
1
125ns
1Mbps
16
10
5
4
NO
2
1
125ns
1Mbps
8
4
3
2
NO
2
1
125ns
500kbps
16
10
5
4
NO
2
2
250ns
250kbps
16
10
5
4
NO
16MHz
2
4
500ns
125kbps
16
10
5
4
YES
1
1
125ns
1Mbps
8
4
3
2
NO
1
1
125ns
500kbps
16
10
5
4
NO
1
1
250ns
250kbps
16
10
5
4
NO
8MHz
2
2
500ns
125kbps
16
10
5
4
NO
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