根据datasheet 第2页的描述：
A logic high on the loopback LBK pin 5 of the SN65HVD233 places the bus output and bus input in a
high-impedance state. The remaining circuit remains active and available for driver to receiver loopback,
self-diagnostic node functions without disturbing the bus
如果将LBK引脚拉高，那么CANH、CANL的电平应该不收引脚D （即CAN的发射）的影响，但实际发现D用波形时，CANH、CANL也有波形。
有没有谁碰到过？
