16.7.1.2 CAN Bit Rate Calculation
Bit-rate is calculated in bits per second as follows:
Time
Bit
2
/
rate
Bit
´
=
BRP
SYSCLKOUT
Where bit-time is the number of time quanta (TQ) per bit. SYSCLKOUT is the device clock frequency, which is
the same as the CPU clock frequency. BRP is the value of BRP
reg
+ 1 (CANBTC.23-16).
Bit-time is defined as follows:
Bit-time = (TSEG1
reg
+ 1) + (TSEG2
reg
+ 1) + 1
In the above equation TESG1
reg
and TSEG2
reg
represent the actual values written in the corresponding fields
in the CANBTC register. The parameters TSEG1
reg
, TSEG2
reg
, SJW
reg
, and BRP
reg
are automatically enhanced
by 1 when the CAN module accesses these parameters. TSEG1, TSEG2 and SJW, represent the values as
applicable per
.
Bit-time = TSEG1 + TSEG2 + 1
16.7.1.3 Bit Configuration Parameters for 45-MHz CAN Clock
This section provides example values for the CANBTC bit fields for some bit rates and sampling points. Note
that these values are for illustrative purposes only. In a real-world application, parameters such as the oscillator
accuracy and the propagation delay introduced by various entities such as the network cable, transceivers/
isolators must be taken into account before choosing the timing parameters.
shows how the BRP
reg
field may be changed to achieve different bit rates with a BT of 15 for a 80%
SP.
Table 16-4. BRP Field for Bit Rates (BT = 15, TSEG1
reg
= 10, TSEG2
reg
= 2, Sampling Point = 80%)
CAN Bus Speed
BRP
CAN Module Clock
1 Mbps
BRP
reg
+1 = 3
15 MHz
500 kbps
BRP
reg
+1 = 6
7.5 MHz
250 kbps
BRP
reg
+1 = 12
3.75 MHz
125 kbps
BRP
reg
+1 = 24
1.875 MHz
100 kbps
BRP
reg
+1 = 30
1.5 MHz
50 kbps
BRP
reg
+1 = 60
0.75 MHz
shows how to achieve different sampling points with a BT of 15.
Table 16-5. Achieving Different Sampling Points With a BT of 15
TSEG1
reg
TSEG2
reg
SP
10
2
80%
9
3
73%
8
4
66%
7
5
60%
Note
For a SYSCLKOUT of 90 MHz, the smallest bit rate possible is 7.031 kbps.
Controller Area Network (CAN)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
1013
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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