D Latch

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One of the main disadvantages of the basic SR latch is that the indeterminate input condition of "SET" = logic "0" and "RESET" = logic "0" is forbidden. This state will force both outputs to be at logic "1", over-riding the feedback latching action and whichever input goes to logic level "1" first will lose control, while the other input still at logic "0" controls the resulting state of the latch. But in order to prevent this from happening an inverter can be connected between the "SET" and the "RESET" inputs to produce another type of flip-flop circuit called a Data Latch. The D flip-flop is by far the most important of the clocked flip-flops as it ensures that ensures that inputs S and R are never equal to one at the same time. D-type flip-flops are constructed from a gated SR flip-flop with an inverter added between the S and the R inputs to allow for a single D (data) input.

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Created on: 05 Mar 2013
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