CAN Bus Frame Extension for Higher Data Capacity
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Solution Overview
Problem
Current CAN bus systems face limitations in data transmission capacity and latency, particularly with increasing demands from modern vehicle systems, as they are optimized for short messages under real-time conditions and struggle with larger data volumes and varying latency requirements.
Innovation Solution
The method modifies the CAN bus protocol by enlarging the data field and adapting the data length code interpretation, allowing for larger data transmission with flexible data field sizes, and using a modified CRC calculation to ensure error detection security, while maintaining compatibility with standard CAN systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the data field size is increased to transmit larger data volumes, then the data transmission capacity is improved, but the compatibility with standard CAN protocols deteriorates
Solution Approach 1:
The patent implements dynamic configuration of the data field size by introducing a data length code (DLC) field that can be set to different values. The system can adaptively switch between standard 8-byte data fields and extended data fields (e.g., 12, 16, 20, 24 bytes) based on communication requirements. This dynamic approach allows the bus system to maintain compatibility with standard CAN protocols when using 8-byte data fields while enabling extended data transmission capacity when needed, thus resolving the contradiction between data capacity and protocol compatibility.
Solution Approach 2:
The patent changes the parameter of data field size from the fixed 8-byte standard to variable sizes (8, 12, 16, 20, 24 bytes) by modifying the interpretation of the DLC field. By defining new mapping relationships between DLC values and data field lengths, the system enables extended data transmission while maintaining a structured approach that preserves protocol organization. This parameter change allows the system to achieve higher data capacity while managing compatibility through defined extension rules.
2Productivity
If the data field is enlarged to more than 8 bytes, then the average data transmission rate is improved, but the device complexity increases
Solution Approach 1:
The patent segments the data field into standard 8-byte portions and extended portions, with the extension occurring in defined increments (4 bytes at a time). This segmentation allows the system to handle extended data transmission by building upon the familiar 8-byte standard structure, making the complexity manageable through modular extension rather than requiring complete redesign of the data handling architecture.
Solution Approach 2:
The extended data field implementation maintains universality by using the same basic CAN protocol structure, arbitration mechanisms, and error handling procedures. The only modification is the data field size parameter, allowing existing CAN controllers and software to work with extended frames by simply recognizing the new DLC values and corresponding data lengths. This multi-functionality approach enables the system to handle both standard and extended data transmissions through a unified protocol framework.
3Reliability
If a modified CRC calculation is used for larger data fields, then the error detection security is improved, but the computation time increases
Solution Approach 1:
The patent implements dynamic CRC calculation where the CRC polynomial degree and calculation method adapt to the data field size. For standard 8-byte data fields, the traditional CRC-15 calculation is used. For extended data fields, the system dynamically selects appropriate CRC parameters (such as CRC-16 or higher) to maintain adequate error detection capability proportional to the data size, thus balancing security requirements with computational efficiency for different data lengths.
Data Source
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AI summary
The invention relates to a method for the serial data transmission in a bus system with at least two participating data processing units. The data processing units exchange messages via the bus, and the transmitted messages have a logical structure in accordance with CAN standard ISO 11898-1, said logical structure comprising 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 comprises a data length code that contains information on the length of the data field. When a first switching condition is present, the data field of the messages can comprise more than eight bytes, deviating from CAN standard ISO 11898-1, wherein the values of the four bits of the data length code are interpreted in a manner at least partly deviating from CAN standard ISO 11898-1 in order to determine the size of the data field when the first switching condition is present.