STM32的CAN波特率计算

波特率=APB1Clock/(1+CAN_BS1+CAN_BS2)/CAN_Prescaler

（PS：CAN_SJW表示重新同步跳跃宽度，不参与波特率的计算，其值可以编程为1到4个时间单元，表示该总线对波特率范围的容差度。公式中1表示同步段固定为一个单位时间。）

eg:APB1Clock=36Mhz,CAN_BS1=3,CAN_BS2=5,CAN_Prescaler=32

     36000k/9/32=125k/s

另外，尽可能地把采样点设置为CiA推荐的值：

CiA波特率75%>800K80%>500K87.5%<=500K

CiA计算方式：(1+CAN_BS1)/(1+CAN_BS1+CAN_BS2)

???采样点设置的影响：采样点设置的符合表格中的范围，CAN通信 会更稳定。

The CAN bit comprises – depending on the configured “atomic” time unit called time quantum (tq) – multiple of these time quanta. The time quanta length derives from the bit-rate prescaler and the used oscillator frequency.

The CAN bit is logically divided into four segments. The synchronization segment has always a length of 1 tq. The following propagation segment and phase-segment 1 are not distinguishable for the user. It is configured as one value. The forth part is the phase-segment 2. Between the two phase-segments, the sample-point is located. If the bit-timing settings move the sample-point to the end of the bit, the propagation segment is enlarged, so that you can realize longer networks. If the sample-point is configured in the other direction, the re-synchronization capability is increased.

The sample point should be the same in all connected CAN nodes. However, in practice it is sufficient if the sample points don't vary too much. The automotive industry has specified some recommendations for the bit timing settings in the SAE J2284 series. For CANopen networks, the recommendations given in CiA 301 should be used. The sample points should be at 87,5 percent of the bit time. For most of the specified bit-rates a range of 85 percent to 90 percent is allowed. Of course, the larger the tolerance range, the shorter the maximum possible length of the network。

CAN位时间组成 取决于配置的“原子”时间单位称为时间量子（tq） - 这些时间量子的倍数。时间量程长度来自比特率预分频器和使用的振荡器频率。
CAN位时间逻辑上分为四个段。同步段总是长度为1 tq。后面的传播段和相位段1对于用户是不可区分的。它被配置为一个值。第四部分是相位段2.在两个相位段之间，定位采样点。如果位定时设置将采样点移动到位的结尾，则传播段被放大，以便可以实现更长的网络。如果采样点在另一个方向配置，则重新同步功能会增加。

所有连接的CAN节点的采样点应该相同。然而，在实践中，如果采样点区别不大就足够了。汽车行业为SAE J2284系列中的位定时设置指定了一些建议。对于CANopen网络，应使用CiA 301中给出的建议。采样点应为位时间的87.5％。对于大多数指定的比特率，允许85％至90％的范围。当然，公差范围越大，网络的最大可能长度越短。