Hard sync
If a CAN node sends data through the bus, it will send a signal indicating the start of communication (that is, the frame start signal described in the next section), which is a falling edge from high to low. When the communication node mounted on the CAN bus does not send data, it will always detect the signal on the bus. As shown in the figure, it can be seen that when the frame start signal appears on the bus, a node detects that the frame start signal of the bus is not within the SS segment of the internal timing of the node, so it judges that its own internal timing is not synchronized with the bus. The data collected at the sampling point is incorrect. Therefore, the node is adjusted in a hard synchronization manner, and the SS segment in its own bit sequence is shifted to the part where the falling edge of the bus occurs to obtain synchronization. After synchronization, the sampling point can collect correct data.