CAN Bit Segmentation

You can understand the big monitoring and bit segments in the below medium story
https://medium.com/@sjindhirapooja/can-bit-segmentation-bit-monitoring-and-bit-segments-9bcd6af249a6

Synchronization Segment

Purpose: Synchronizes various nodes in the network.

Details:

• CAN protocol is asynchronous, lacking a separate clock signal.
• The frame itself acts as the synchronization source.
• The synchronization segment is where the transmitting node (Tx) places the bit on the bus.
• When the bit value is received, receiving nodes (Rx) synchronize with the transmitting node.

Propagation Segment

Propagation Delay

• Example Setup: Consider a 1 Mbps, 40m bus with Node A at one end and Node B at the other end.
• Signal Travel Time: When a bit is placed on the bus, it takes some time for Node B to receive the information due to signal travel time, which depends on the medium (e.g., copper or aluminum wires), wire quality, and resistance. This delay is known as propagation delay.

Propagation Delay

• CAN uses a twisted pair physical medium and is an asynchronous communication protocol.
• In the above image, all four segments are present. The junction of Phase 1 and Phase 2 is the sampling point.
• Node A is the transmitter (Tx), and Node B is the receiver (Rx).
• Initially, the bus value is recessive (1). Node A wants to place a dominant bit (0) on the bus, causing a high-to-low transition during the synchronization segment.
• The value 0 is placed on the bus during the synchronization segment.
• The change travels from Node A to Node B, causing a propagation delay. The difference in time between when Node A places the edge on the bus and Node B senses it is called propagation delay.

Sampling Point and Propagation Segment

• Without Propagation Segment: If there were no propagation segment, the sampling point would come too early, causing Node A to sample the bit value as recessive, while Node B samples it as dominant. Thus, without a propagation segment, sampling would occur before the propagation to Node B is complete.
• Ensuring Consistency: The propagation segment ensures that all nodes receive the same bit value transmitted by the transmitter node.
• Determining Segment Length: The propagation segment is determined such that t_prop >= t_ABmax (where t_ABmax is the maximum propagation delay).
• This ensures that even if the transmitter node transmits the bit at the end of the synchronization segment, all Rx nodes will have received the bit before the propagation segment ends.

The propagation segment ensures all nodes receive the same bit value which the transmitter node has transmitted on the bus.

Phase Segments 1 and 2

Purpose: Determine the sampling point within the bit.

Details:

• These segments act as buffers to adjust the sampling point.
• If you increase Phase Segment 1 and decrease Phase Segment 2, the bit sampling point moves to the right of the bit.
• If you decrease Phase Segment 1 and increase Phase Segment 2, the bit sampling point moves to the left of the bit.
• The junction of PH1 and PH2 is the sampling point of the bit on the bus.

Conclusion

By understanding these segments, one can ensure accurate data transmission and reception in a CAN network. Each segment plays a pivotal role in maintaining synchronization, compensating for propagation delays, and determining the precise sampling point.