Fast CAN Data Frame Segmentation for High-Speed Transmission
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Solution Overview
Problem
Current CAN protocols face limitations in transmitting large data blocks efficiently, leading to delays and impaired real-time properties, as they require bit-by-bit arbitration and have a low bit rate, which cannot be easily increased without disrupting the network or compromising error detection and consistency.
Innovation Solution
A modified data transmission method, referred to as Fast CAN, which allows temporal bit length to assume two different values within a data frame, using different scaling factors between the bus time unit and the oscillator clock, enabling faster data transmission while maintaining essential CAN properties like error detection and network consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bit rate is increased by reducing the duration of each bit, then data transmission speed is improved, but the real-time properties and network consistency are compromised because all bus participants must have a uniform image of the bus status
Solution Approach 1:
The data frame is segmented into two distinct parts: an arbitration field transmitted at the standard bit rate (500 kbit/s) to maintain network consistency, and a data field transmitted at the increased bit rate (1.15 Mbit/s) to achieve faster data transmission. This segmentation allows different transmission rates to coexist within the same communication protocol.
Solution Approach 2:
The system dynamically switches between two operating modes: standard CAN mode for arbitration and fast transmission mode for data transfer. The communication interface can be temporarily switched to another communication mode allowing relatively high bit rate, and then switched back to ensure proper transmission confirmation and maintain network consistency.
2Productivity
If temporary switching to high bit rate mode is used to transmit large data blocks, then transmission speed is improved, but communication with CAN protocols is interrupted and real-time properties are impaired
Solution Approach 1:
The arbitration field is transmitted continuously at the standard bit rate to maintain ongoing CAN protocol communication and network consistency. Only the data field portion is transmitted at the higher bit rate, allowing continuous arbitration functionality while achieving faster overall data block transmission.
3Speed
If the duration of transmitted bits is reduced to increase bit rate, then data transmission rate is improved, but the minimum duration required for bit-by-bit arbitration cannot be observed
Solution Approach 1:
Different parts of the data frame have different transmission qualities: the arbitration field uses the standard, slower bit rate to ensure proper arbitration functionality and network consistency, while the data field uses the faster bit rate to achieve high-speed data transmission. Each part is optimized for its specific function.
Data Source
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AI summary
A method and an apparatus are specified in order to allow larger amounts of data to be transmitted relatively quickly in a network. According to the invention, the object is achieved in that the transmitted data frames have a logic structure in accordance with CAN Specification ISO 11898-1, wherein the time bit length within a data frame can assume at least two different values, wherein, for a first predeterminable area within the data frame, the time bit length is greater than or equal to a predetermined minimum value of approximately one microsecond, and in at least one second predeterminable area within the data frame, the time bit length is at least half, and preferably less than half, with respect to the first area, wherein changes in the time bit length are achieved by use of at least two different scaling factors for setting the bus time unit relative to a shortest time unit or the oscillator clock during operation.