Summary

• Memory elements can be constructed by appropriately feeding back the output of gates to the input.
• The most basic memory element is an RS flip flop which consists of two NOR gates.
• By adding two more gates (and an inverter) we can construct a D-flipflop.
• The D-flipflop has an Enable input and a data input.
• When the Enable input is 1, the data input is read into the flipflop.
• When the Enable input is 0, the currently stored value is held regardless of the data input.
• D-flipflops can be used to construct sequential logic circuits such as counters or shift-registers.