For this lab you will build a "flipflop" memory circuit that can store one bit of information. This style of memory is very fast but relatively expensive, and is thus used mostly for small-scale storage on the same chip as the main processor. (The bulk of a computer's working memory is built using a different, less expensive circuit based upon capacitors rather than logic gates, which we won't directly study. However, if expense were not important you could build an entire memory using only flipflops.)
Preparation
So that you may save your work, you should download the circuit simulator to your H drive or other storage and run the downloaded file, instead of launching it from the web page. Otherwise the Save button will report an error. Test the save button to be sure it works before you start the lab below.
Basic Flipflop
First build the basic flipflop, shown at right. Notice that it includes a feedback loop, where part of the output is redirected back to the input. This feedback allows the circuit to keep a persistent output state, either on or off, once the circuit has been placed in that state. Pulses on the two input wires alter the state; turning the top input on then off puts the flipflip in the on state, while pulsing the bottom input on then off puts the flipflop in the off state.
Load-Control Memory
The flipflop retains its output state, but the inputs are somewhat inconvenient. It would be nicer to have a single input wire, whose state can be stored in the flipflop when desired. A pulse on a second control wire will activate the storage. The circuit at right achieves this goal. Build it and experiment with the controls.