Sunday, 19 February 2012

Flip-Flops contd..

Edge Triggered D Flip-flop:
  • All the master slave flip-flops function well, only when pulse signal is applied as enable signal. We can call them as pulse triggered devices. If there is only single transition on enable signal, then they can’t work.
  • Edge triggered flip-flops works with single transition on enable signal (CLK).
Important Parameters of flip-flop:
Set-up time (Ts): The period of time immediately preceding the enable signal transition during which excitation input must be held stable.
Hold Time (Th): Period of immediately following enable signal transition during which excitation input must be stable. 
Latches Vs Flip-flops:
  • Both latches and flip-flop stores a single bit of information
  • The difference between them is latch is level triggered and flip-flop is edge triggered
  • For a flip-flop only at clock edge (either +ve edge or –ve edge) depending on flip-flop excitation input flip-flop state changes. But in case of latch as long as clock input is high, its output changes according to its excitation inputs.
Consider D latch and D flip-flop. The outputs of both the devices are shown below for given excitation input D.

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