RS485 Interface Access State Detection Circuit
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Solution Overview
Problem
Existing RS485 interface circuits fail to detect shorted or open faults and monitor access states, leading to self-transmitting self-receiving (STSR) unwanted data issues due to the lack of polarity distinction and fault detection mechanisms.
Innovation Solution
A detection circuit comprising a polarity determination circuit, timer circuit, driver circuit, receiver circuit, and test output circuit, which determines the access state by setting functional states, clearing timers, and controlling output enable signals to prevent STSR by maintaining received data at a default level in output states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the driver output enable signal DE is valid and the receiver input enable signal RE is valid simultaneously, then the RS485 interface can transmit and receive data, but self-transmitting self-receiving (STSR) unwanted data appear
Solution Approach 1:
The patent applies preliminary action by detecting the access state of the RS485 interface before enabling normal data transmission. The detection circuit determines whether another device is connected to the interface, and only after successful detection does the system enable the driver output enable signal DE and receiver input enable signal RE simultaneously. This preliminary detection prevents STSR unwanted data from occurring during subsequent transmission operations.
2Adaptability or versatility
If polarity determination and adjustment circuit is added to distinguish polarities of signal lines, then non-polarized RS485 interface can be implemented, but device complexity increases
Solution Approach 1:
The patent implements polarity determination and adjustment as a preliminary action before normal data transmission. The detection circuit includes components that automatically detect and adjust polarity during the access state detection phase. Once polarity is determined and adjusted, the system proceeds to normal transmission without requiring continuous complex polarity management, thus achieving adaptability while controlling overall complexity.
3Reliability
If fault detection mechanism is added to detect shorted or open faults, then interface reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges fault detection functionality with the access state detection circuit. The same detection circuit that determines whether a device is connected to the RS485 interface also detects shorted or open faults by analyzing the electrical characteristics during the detection phase. This merging approach improves reliability through comprehensive fault detection while avoiding the need for separate dedicated fault detection circuits, thus controlling device complexity.
Data Source
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AI summary
The present disclosure provides a detection circuit for an access state of an RS485 interface and a detection method for an access state of an RS485 interface. The detection circuit for an access state of an RS485 interface includes a polarity determination circuit, a timer circuit, a driver circuit, a receiver circuit, and a test output circuit, where a functional state setting signal ST input terminal of the polarity determination circuit is configured to input a functional state setting signal ST; a timer clearing signal CL output terminal of the polarity determination circuit is connected to a timer clearing signal CL input terminal of the timer circuit; a timer overflow indication signal OV input terminal of the polarity determination circuit is connected to a timer overflow indication signal OV output terminal of the timer circuit; a transmitted data input signal input terminal of the polarity determination circuit is configured to input a transmitted data input signal XD; and a received data output signal input terminal of the polarity determination circuit is connected to a received data output signal RD output terminal of the receiver circuit.