CAN标准中的时钟容差修正建议

Modification Suggestions on Clock Tolerance in CAN Standard

在CAN标识符的仲裁阶段,由于传输延时的存在,发送显位的节点无法看见快节点迟到的隐位/显位跳变沿,因此发送节点间无法建立同步。在最坏情况下,快的发送节点在最后一位退出,它可能一直没有与胜出的慢节点同步,直至ID后的第1个隐位/显位跳变沿。这就使正确同步所需的时钟容差大幅度减小,这是原CAN标准ISO11898-1:2003以及一致性测试标准ISO16845:2004未考虑到的。本文分析了这种情况,提出了修正建议。

In the arbitration process of CAN ID,The transmitter sending dominant bit can not see the late recessive-to-dominant edge sent by the faster transmitter due to propagation delay.Hence,transmitters can not be synchronized.In the worst case,the faster transmitter gives up at the last bit of ID,not synchronized with the winning slow transmitter till the first recessive-to-dominant edge after arbitration.This greatly reduces the clock tolerance.The case is considered in ISO 11898-1：2003 and ISO 16845：2004.This paper analyses the situation and gives corresponding suggestions.