CAN 波特率设置

CAN时钟源的选择有两种，一种为总线时钟，一种为外接时钟

 

波特率计算公式：F(Baud) = F/(BRP* (1+TSEG2+TSEG1))

 

波特率设置相关寄存器

 

7	6	5	4	3	2	1	0
SJW1	SJW0	BRP5	BRP4	BRP3	BRP2	BRP1	BRP0

Table1 CANBTR0

 

SJW1	SJW0	Synchronization  Jump Width
0	0	1  Tq clock cycle
0	1	2  Tq clock cycle
1	0	3  Tq clock cycle
1	1	4 Tq clock cycle

Table2 SJW

 

BRP5	BRP4	BRP3	BRP2	BRP1	BRP0	Prescaler value
0	0	0	0	0	0	1
0	0	0	0	0	1	2
0	0	0	0	1	1	3
0	0	0	1	1	1	4
..	..	..	..	..	..	..
1	1	1	1	1	1	64

Table3 Baud Rate Prescaler

 

7	6	5	4	3	2	1	0
SAMP	TSEG22	TSEG21	TSEG20	TSEG13	TSEG12	TSEG11	TSEG10

Table4 CANBTR1

 

TSEG22	TSEG21	TSEG20	Time  Segment 2
0	0	0	1
0	0	1	2
..	..	..	...
1	1	0	7
1	1	1	8

Table5 TSEG2

 

TSEG13	TSEG12	TSEG11	TSEG10	Prescaler value
0	0	0	0	1
0	0	0	1	2
0	0	1	0	3
0	0	1	1	4
..	..	..	..	..
1	1	1	0	15
1	1	1	1	16

例程

1.        总线时钟40MHZ，设置CAN波特率为500KHZ

40MHZ/500KHZ=80

80 = BRP *(1+TSEG2+TSEG1) =10 * 8;

所以设置BRP =8,TSEG2=4,TSEG1=5. SJW=0x01对应寄存器值

CAN0BTR0=0x47;                                                                           

CAN0BTR1=0x43;

2.        总线时钟40MHZ，设置CAN波特率为250KHZ

40MHZ/250KHZ=16

80 = BRP *(1+TSEG2+TSEG1) =16 * 8;

所以设置BRP =8,TSEG2=4,TSEG1=5,SJW=0x01对应寄存器值

CAN0BTR0=0x4F;                                                                            

CAN0BTR1=0x43;