CAN XL Transceiver Protocol Adaptation
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Solution Overview
Problem
The introduction of the CAN XL protocol poses challenges in backwards compatibility with existing CAN FD devices, as the different voltage level schemes can lead to misinterpretation of signals and premature exit from the protocol exception state in CAN FD controllers.
Innovation Solution
The proposed solution involves a CAN XL transceiver that autonomously switches between the CAN FD and CAN XL voltage level schemes based on observed bus voltage levels, ensuring that CAN FD controllers remain in the protocol exception state until CAN XL frames are complete, thereby maintaining compatibility and preventing signal integrity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a CAN transceiver uses a fixed voltage level scheme for CAN FD protocol, then the device operates reliably within the standardized protocol, but it cannot support the extended CAN XL protocol with different voltage levels
Solution Approach 1:
The transceiver dynamically switches between CAN FD and CAN XL voltage level schemes based on the operational mode. The receiver arrangement can adjust its threshold voltages and signal interpretation logic to match the active protocol, allowing a single device to support multiple protocols without requiring separate hardware for each protocol variant.
Solution Approach 2:
The transceiver changes its electrical parameters (voltage thresholds, differential voltage levels) depending on the detected protocol mode. When operating in CAN XL mode, the receiver uses different voltage reference levels compared to CAN FD mode, enabling compatibility with both standardized and extended protocols through parameter adaptation rather than hardware modification.
2Reliability
If a CAN FD controller detects voltage levels using standardized thresholds, then it ensures reliable communication according to ISO 11898-1, but it may misinterpret CAN XL signals and exit the protocol exception state prematurely
Solution Approach 1:
The receiver arrangement acts as an intermediary between the physical bus signals and the CAN FD controller. It translates the raw differential voltage signals into protocol-appropriate logic levels, using mode-dependent threshold comparison. This intermediary layer prevents the controller from directly interpreting raw voltage levels, thereby avoiding misinterpretation of CAN XL signals as valid CAN FD recessive states.
Solution Approach 2:
The receiver arrangement incorporates feedback mechanisms to monitor the bus state and adjust its signal interpretation accordingly. By continuously monitoring differential voltage levels and comparing them against mode-specific thresholds, the receiver can detect when CAN XL signaling is active and maintain the controller in the protocol exception state, preventing premature exit based on misinterpreted voltage levels.
Data Source
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AI summary
A Controller Area Network (CAN) transceiver includes a receiver configured to determine a voltage differential signal from analog signalling received from a CAN bus and configured to provide a digital output signal at a receiver output to a CAN controller based on the voltage differential signal. The receiver includes arming circuitry configured to place the receiver in an armed or unarmed state based on the voltage differential signal, a first threshold corresponding to a first CAN protocol, and a second threshold corresponding to a second CAN protocol. When the receiver is in the unarmed state, a first digital signal indicative of activity on the CAN bus is provided based on a comparison between the voltage differential signal and the first threshold, and when in the armed state, the first digital signal is provided based on comparisons between the voltage differential signal and each of the first and the second thresholds.