CAN FD Transmission Unit Segmentation for Mixed Bus Networks
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Solution Overview
Problem
In mixed CAN bus networks, the presence of Classic CAN users causes communication to revert to slower Classic CAN format due to incompatibility with CAN FD messages, leading to errors and reduced bandwidth, as unmodified Classic CAN communication controllers cannot handle the faster data bits of CAN FD messages.
Innovation Solution
A transmission unit that receives messages with a predefined control signal, forwarding the first bit sequence to a processing station and sending a terminating bit sequence instead of the second bit sequence if the control signal deviates from the predefined value, allowing for separate handling of CAN FD and Classic CAN messages and enabling mixed operation without errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CAN FD messages are transmitted in a mixed network with Classic CAN users, then transmission bandwidth and data rate are improved, but Classic CAN controllers generate errors and communication reliability deteriorates
Solution Approach 1:
The transmission unit segments the bus communication into two distinct paths: one for CAN FD messages and another for Classic CAN messages. By checking the control signal in received messages, the transmission unit determines whether to forward the complete message or send only a terminating bit sequence, thereby segmenting the message flow to prevent incompatibility errors between CAN FD and Classic CAN controllers in the mixed network
Solution Approach 2:
The transmission unit acts as an intermediary device between CAN FD transmitters and Classic CAN receivers. It intercepts CAN FD messages, checks their control signals, and selectively transforms or terminates them before forwarding to Classic CAN controllers, preventing errors while maintaining network compatibility and enabling both protocols to coexist reliably
2Speed
If CAN FD protocol is implemented to increase bit rate, then transmission speed is improved, but compatibility with Classic CAN controllers is lost
Solution Approach 1:
The transmission unit dynamically adjusts its behavior based on the received message type. When a CAN FD message is detected (via control signal checking), it dynamically switches to sending a terminating bit sequence instead of the full message, adapting to the capabilities of Classic CAN controllers while preserving CAN FD high-speed communication capabilities when appropriate
Solution Approach 2:
The transmission unit changes the parameter of the transmitted message from complete CAN FD message format to a simplified terminating bit sequence format when Classic CAN controllers are detected. This parameter change maintains protocol compatibility while preserving the ability to utilize CAN FD high bit rates for appropriate message types
Data Source
AI summary
A transmission unit for connection to a first bus system, the transmission unit receiving messages via the first bus system, the messages being constructed as a succession of a first bit sequence, of at least one control signal and of a second bit sequence, the first bit sequence of a received message being forwarded by the transmission unit to a processing station, at least one predefined control signal of the received message being checked by the transmission unit, the second bit sequence of the received message being forwarded by the transmission unit to the processing station if the predefined signal of the received message has a predefined value, instead of the second bit sequence, the transmission unit sending a predefined or predefinable terminating bit sequence to the processing station, if the predefined control signal of the received message has a value that deviates from the predefined value.