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Codiode/Problems/Sequential Logic

Basic Falling Edge Detector

EasyLogic CircuitBuild

Communication protocols like UART and I2C rely on detecting a high-to-low transition on the data line to signal the start of a transaction. A synchronous edge detector safely flags this event for exactly one clock cycle without introducing combinational glitches.

The circuit must monitor the din signal and assert pulse to 1 during the exact clock cycle that a 1-to-0 transition is detected. The detection compares the current state of din against its state from the previous clock cycle.

| din (previous) | din (current) | pulse | |------------------|-----------------|---------| | 0 | 0 | 0 | | 0 | 1 | 0 | | 1 | 0 | 1 | | 1 | 1 | 0 |

Constraints

  • Use exactly one D flip-flop to store the previous state of the input.
  • Derive the output using only the current input and the registered previous input.
  • Do not use asynchronous delay chains or series inverters to create timing delays.

Topics

Sequential LogicSynchronizationEdge Detection

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