SR Latch, they are cool

So starting with the building blocks of digital memory we have an SR Latch (Set Reset).

This latch allows you to set and toggle the out put and reset the out put.

This version is made up of two NAND gates where the output of one feeds the input of the other. And there are two outputs Q and Not Q.

The inputs of this Latch are Active Low, which means S and R need to normally be High and data is entered by pulling S Low, and Resetting by pulling R Low. Side not pulling S and R Low at the same time is not good because if they are let back high at the same time, there is know way to predict what the out put will be.

Designing the circuit is is quite simple.

On the left we have 2 10k pull up resistors, which get sunk to GND by the switch's S and R. Then we have the first NAND Gate with its output LED, then we have the second NAND gate and its output LED.

Here is the setup on a breadboard (it works).