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CAN時(shí)鐘源的選擇有兩種，一種為總線時(shí)鐘，一種為外接時(shí)鐘 波特率計(jì)算公式：F(Baud) = F/(BRP* (1+TSEG2+TSEG1)) 波特率設(shè)置相關(guān)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. 總線時(shí)鐘40MHZ，設(shè)置CAN波特率為500KHZ 40MHZ/500KHZ=80 80 = BRP *(1+TSEG2+TSEG1) =10 * 8; 所以設(shè)置BRP =8,TSEG2=4,TSEG1=5. SJW=0x01對(duì)應(yīng)寄存器值 CAN0BTR0=0x47; CAN0BTR1=0x43; 2. 總線時(shí)鐘40MHZ，設(shè)置CAN波特率為250KHZ 40MHZ/250KHZ=16 80 = BRP *(1+TSEG2+TSEG1) =16 * 8; 所以設(shè)置BRP =8,TSEG2=4,TSEG1=5,SJW=0x01對(duì)應(yīng)寄存器值 CAN0BTR0=0x4F; CAN0BTR1=0x43;
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