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A D Latch is a basic type of latch that has only one input. One can construct this latch by adding an inverter to a SR Latch:

         +--------+              C D |  Y
D--+-----|S   Y(H)|---Y(H)       ----+-------
   |     |        |              0 - | rest
   |     |        |              1 0 |  0
   |     |        |              1 1 |  1
   +-|>o-|R   Y(L)|o--Y(L)
         |        |
C--------|C       |

The behavior here is similar to the SR Latch, except the S and R inputs are both controlled by D. This means that, whenever C=1, the output Y follows the input D (after the propagation delay), and when C=0, the latch closes, or "latches" onto the last value that was placed upon D. Thus this device can be used as a kind of primitive memory, although the stability of the D Latch is much worse than any sort of Flip-Flop.

See also SR Flip-Flop, D Flip-Flop.