D Latch

In electronics, a latch is a kind of bistable multivibrator, an electronic circuit that has two stable states and therefore can store one bit of information. Today the word is mainly used for simple transparent storage elements, while slightly more advanced non-transparent (or clocked) devices are described as flip-flops. Informally, as this distinction is quite new, the two words are sometimes used interchangeably.[citation needed]

A circuit incorporating latches has state; its output depends not only on its current input, but also on its previous inputs. Such a circuit is described as sequential logic.

This latch is closely related to the gated SR latch and can be similarly constructed. It is also known as transparent latch, data 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.

Transparent latches are typically used as I/O ports or in asynchronous systems.[nb 2] They are available as integrated circuits, usually with multiple latches per circuit. For example, 74HC75 is a quadruple transparent latch in the ubiquitous 7400 series.

D-latch truth table

E/C   D       Q       Q       Comment

0       X       Qprev        Qprev        No change

1       0       0       1       Reset

1       1       1       0       Set