Variable Bit Length CAN Data Frame Transmission
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Solution Overview
Problem
Current CAN bus systems face limitations in transmitting large data blocks while maintaining real-time conditions due to low bit rates, and existing solutions either disrupt communication protocols or degrade real-time performance.
Innovation Solution
The method involves temporarily reducing the bit length within a data frame after arbitration, increasing the clock-pulse rate for a limited period, and communicating this change to receivers through identification within the data frame, allowing for flexible bit rate adjustment without compromising real-time performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bit rate is increased by reducing the duration of individual bits, then the transmission speed of large data blocks is improved, but the real-time characteristics and uniform access to bus state are degraded
Solution Approach 1:
The data frame is segmented into two distinct parts: an arbitration field transmitted at the standard bit rate for maintaining real-time characteristics and bus state uniformity, and a data field transmitted at an increased bit rate for efficient large data block transmission. This segmentation allows each part to serve its specific function optimally without compromising the other.
Solution Approach 2:
The system dynamically adjusts the bit rate based on the phase of data transmission. During the arbitration phase, the standard bit rate is maintained to ensure all bus users have uniform access to the bus state. During the data transmission phase, the bit rate is increased to improve transmission speed. This dynamic adaptation resolves the contradiction between speed and reliability.
2Productivity
If a different communication mode is used for transmitting large data blocks, then the transmission rate is improved, but the communication protocol continuity and real-time performance are disrupted
Solution Approach 1:
The CAN bus system is designed to handle two different transmission modes within a single communication protocol framework. The same bus infrastructure and basic protocol mechanisms are used for both standard real-time communication and high-speed data block transmission, eliminating the need for separate communication modes or protocol switching.
Solution Approach 2:
Instead of switching to a different communication mode, the system changes the bit rate parameter within the existing CAN protocol framework. The arbitration field and data field use different bit rates, but both are part of the same protocol structure, maintaining protocol continuity while achieving high transmission rates for large data blocks.
3Loss of time
If the bit length is reduced for faster transmission, then the data quantity transmission speed is improved, but the arbitration correctness and bus state uniformity are compromised
Solution Approach 1:
The transmission is segmented into arbitration phase and data phase, with each phase using appropriate bit lengths. The arbitration field uses standard bit lengths to ensure precise arbitration and uniform bus state picture, while the data field uses reduced bit lengths to minimize transmission time loss.
Solution Approach 2:
The arbitration field is transmitted first at standard bit rate to establish correct arbitration and synchronize all bus users before the high-speed data transmission begins. This preliminary action ensures that all users have a uniform picture of the bus state before switching to the faster transmission mode.
Data Source
AI summary
A method for serially transmitting data in a bus system having at least two bus users, which exchange data frames over the bus, the bus users deciding which data frames they receive, as a function of an identifier, the data frames having a logic structure according to the CAN standard, ISO 11898-1, the temporal bit length (L1, L2) inside of a data frame being able to assume at least two different values, the temporal bit length (L1) for at least one first, specified or specifiable region within the data frame meeting the requirements of the CAN standard, ISO 11898-1, the temporal bit length (L2) in at least one second, specified or specifiable region being reduced in comparison with the first region, and a change in the temporal bit length being signaled by the sender, using an identification (310) contained in the same or one of the preceding data frames.