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Codiode/Problems/Sequential Logic

Minimum Pulse Width: Setup Plus Hold Constraint

HardLogic CircuitAnalyze

Synchronizing short asynchronous pulses like interrupts or button presses requires strict timing to ensure the receiving flip-flop can reliably capture the event. A signal must remain stable through a specific window of time around the clock edge to avoid metastability.

A rising-edge triggered D flip-flop receives an asynchronous data pulse on input D and is clocked by signal CLK. The flip-flop has a setup time t_setup of 2 time units and a hold time t_hold of 1 time unit. The clock period is significantly longer than the pulse width.

Evaluate the minimum pulse width required on D to prevent the pulse from being completely swallowed by the timing requirements. Identify the alignment scenarios that cause timing violations.

Constraints

  • t_setup is exactly 2 time units.
  • t_hold is exactly 1 time unit.
  • The asynchronous pulse on D arrives randomly relative to the active edge of CLK.

Topics

Setup TimeHold TimePulse WidthSynchronization

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