Latches are designed to be transparent. That is, input signal changes cause immediate changes in output. Flip-flops, on the other hand, have their content change only either at the rising or falling edge of the clock signal. After the rising or falling edge of the clock, the flip-flop content remains constant even if the input changes
The D latch as shown below has an enable input. When the E input is 1, the Q output follows the D input. In this situation, the latch is said to be "open" and the path from the input D to the output Q is "transparent". Thus the circuit is also known as a transparent latch. When E is 0, the latch is disabled or "closed", and the Q output retains its last value independent of the D input.
The truth table and diagram
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