CAN Bus Frame Switching for Higher Data Capacity
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Solution Overview
Problem
Current CAN bus systems face limitations in data transmission capacity and latency, particularly in modern vehicle networks, where increased data demands for safety and comfort systems require higher data transmission rates and reduced latency.
Innovation Solution
The method enhances data transmission by allowing the data field of CAN messages to exceed the standard 8 bytes, using additional values of the data length code to determine the data field size, and incorporating a modified CRC calculation that includes stuff bits for error detection, while maintaining compatibility with standard CAN systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the data field size is limited to 8 bytes according to CAN standard, then compatibility with standard CAN systems is maintained, but data transmission capacity is insufficient for modern vehicle networks
Solution Approach 1:
The patent implements dynamic switching between standard CAN mode (8-byte data field) and extended CAN mode (up to 128-byte data field) based on the R0 bit value in the control field. This allows the system to adapt its data transmission capacity dynamically, maintaining compatibility with standard CAN systems when R0=0 while enabling extended data capacity when R0=1
Solution Approach 2:
The patent changes the interpretation parameter of the R0 bit in the control field from its standard CAN function to a mode selection indicator. When R0=1, the system interprets the data length code (DLC) differently to support extended data field sizes up to 128 bytes, thereby increasing data transmission capacity without affecting standard CAN operation when R0=0
2Productivity
If multiple subscriber stations transmit simultaneously via bit-wise arbitration, then channel utilization is improved, but transmission latency increases for high-priority messages
Solution Approach 1:
The patent introduces time-triggered communication as a periodic action alternative to the event-driven bit-wise arbitration. In TTCAN mode, time slots are pre-allocated to different subscriber stations, ensuring that high-priority messages transmit at predetermined times without arbitration delays, while maintaining overall channel utilization through structured periodic access
3Quantity of substance
If the data length code is reinterpreted to support larger data fields, then data transmission capacity increases, but complexity of protocol interpretation increases
Solution Approach 1:
The patent enables receiving stations to automatically determine the correct DLC interpretation mode by checking the R0 bit value in the control field. When R0=1, the receiver automatically applies the extended DLC interpretation table to calculate the actual data field size, eliminating the need for manual configuration or complex external control logic
Data Source
AI summary
A method is described for serial data transmission in a bus system having at least two subscribed data processing units that exchange messages via the bus, the transmitted messages having a logical structure in accordance with CAN standard ISO 11898-1, the logical structure including a start-of-frame bit, an arbitration field, a control field, a data field, a CRC field, an acknowledge field and an end-of-frame sequence, the control field including a data length code, which contains information regarding the length of the data field. When a first switchover condition is satisfied, the data field of the messages, in contrast to CAN standard ISO 11898-1, may comprise more than eight bytes, the values of the four bits of the data length code being interpreted at least partially in deviation from CAN standard ISO 11898-1 for determining the size of the data field when the first switchover condition is satisfied.