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.