Experiment 16 - The latch II

Now, you expand your RS latch. In this way you change the behavior and thus the logic of the latch. This helps you understand how to store information with Boolean logic.

Consider the circuit diagram shown. You recognize the RS latch and the extension. The extension avoids the undefined state (R=1, S=1). Also the inputs are renamed to D and E, where D stands for "DATA" and E for "ENABLE".

D E Q Q' 0 0 0 1 1 0 1 0 0 1 stored 1 1 stored Truth Table DE Latch.

Circuit Diagram DE Latch.

Also the truth table has changed...

• If E is set to 0, you can use D to switch freely between Q and Q'... Q follows D. Q' shows the opposite result.
• If E is put to 1, the circuit stores the last value of Q and Q'.

Circuit of a DE Latch. (Enlarge)

Image now, you want to store a piece of information (D). For this you swiitch E to 0, you enter the information by using D and put E back to 1. Now your information is stored. Flip flops are very versatile and can be found in a variety of digital applications. But more about this in other topics. For the moment this was the last experiment on this topic...