Common I/O Terminal Circuit Using Latched States to Prevent Hazards
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Solution Overview
Problem
Conventional common input/output terminal control circuits face hazards during switching operations due to timing delays, leading to potential malfunctions, especially in CPU chips with increased I/O pins, requiring complex software sequences to mitigate these issues.
Innovation Solution
A common input/output terminal control circuit design incorporating data and direction selection circuits, holding circuits, and an output circuit that delays data or direction signals to prevent hazards by using previous signal states, eliminating the need for software sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional common input/output terminal control circuit is used, then the I/O pin can be shared by multiple circuits, but hazard output occurs during switching operations due to timing delays
Solution Approach 1:
The patent applies preliminary action by comparing the selection signal with a previously latched selection signal before completing the switching operation. The hazard prevention circuit detects potential hazards in advance by comparing current and previous states, and only allows switching to proceed when the comparison indicates safety. This prevents hazard outputs by performing the safety check before the actual switching occurs.
2Reliability
If software sequences are used to prevent hazard outputs, then switching reliability improves, but device complexity and operation complexity increase
Solution Approach 1:
The patent applies self-service by implementing an automatic hazard detection and prevention mechanism within the control circuit itself. The hazard prevention circuit continuously monitors the selection signal and automatically compares it with the previously latched signal, eliminating the need for external software sequences. The circuit serves itself by detecting and preventing hazards through internal logic operations, thereby reducing operational complexity while maintaining reliability.
3Reliability
If software sequences are used to prevent hazard outputs, then switching reliability improves, but ease of operation deteriorates due to required control steps
Solution Approach 1:
The hazard prevention circuit automatically performs safety checks by comparing the current selection signal with the previously latched signal, eliminating the need for manual software control steps. The circuit monitors itself and prevents hazards without requiring external intervention or complex sequencing, thereby maintaining reliability while significantly improving ease of operation.
4Stability of the object's composition
If the selection signal is latched on clock rising edge, then the latch circuit operates synchronously, but hazard output occurs during the delay period between signal change and latching
Solution Approach 1:
The patent applies preliminary action by performing a safety comparison between the current selection signal and the previously latched signal before the latching operation completes. The hazard prevention circuit detects potential hazards in advance during the delay period, and only allows the latched signal to be output when the comparison indicates safety. This maintains synchronous operation while preventing hazard outputs during the vulnerable delay period.
Data Source
AI summary
A first data selection circuit selects a data signal among a plurality of data signals from a plurality of circuits, a first direction selection circuit selects a direction control signal of the same circuit among a plurality of direction control signals from these circuits. A data holding circuit and a direction holding circuit respectively hold the selected data signal and direction control signal. A second data selection circuit selects a data signal from the first data selection circuit or the data holding circuit. A second direction selection circuit selects the direction control signal from the first direction selection circuit or the direction holding circuit. An output circuit outputs, to a common input/output terminal, the data signal from the second data selection circuit in accordance with the direction control signal from the second direction selection circuit.