D flip flop
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Author: Rajan

Forked from: Rajan/D flip flop

Project access type: Public

Description:

This latch exploits the fact that, in the two active input combinations (01 and 10) of a gated SR latch, R is the complement of S. The input NAND stage converts the two D input states (0 and 1) to these two input combinations for the next SR latch by inverting the data input signal. The low state of the enable signal produces the inactive "11" combination. Thus a gated D-latch may be considered as a one-input synchronous SR latch. This configuration prevents application of the restricted input combination. It is also known as transparent latchdata latch, or simply gated latch. It has a data input and an enable signal (sometimes named clock, or control). The word transparent comes from the fact that, when the enable input is on, the signal propagates directly through the circuit, from the input D to the output Q. Gated D-latches are also level-sensitive with respect to the level of the clock or enable signal.

Transparent latches are typically used as I/O ports or in asynchronous systems, or in synchronous two-phase systems (synchronous systems that use a two-phase clock), where two latches operating on different clock phases prevent data transparency as in a master–slave flip-flop.

Latches are available as integrated circuits, usually with multiple latches per chip. For example, 74HC75 is a quadruple transparent latch in the 7400 series.

The truth table below shows that when the enable/clock input is 0, the D input has no effect on the output. When E/C is high, the output equals D.

Gated D latch truth tableE/CDQQComment0XQprevQprevNo change1001Reset1110Set

Symbol for a gated D latch


Created: Jul 05, 2023

Updated: Aug 27, 2023


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