# Fundamental Circuits in Computer Technology.

A full study of digital logic circuits is beyond the scope of this basic introduction, however we will consider three basic circuits which are very important in computer systems.

## A one bit memory circuit.

A latch is a simple digital circuit where the output can be set to either logic 1 or logic 0 by an input signal. The circuit then remains in/“remembers” this state even after the input is removed. This is a memory circuit that can “remember” a single binary digit (bit). Circuits similar to this, form the building blocks, for the RAM memory that is used in all modern computer systems. From the truth table with the logic circuit above, we can see that:

• When the inputs S and R are both at logic 0, the output of Q remains in whatever state it was to begin with (Qi).
• If the set input S is 1 while the reset input R is zero, the output Q is set to 1.
• If the Reset input R is 1 while the set input S is zero, the output Q is reset to 0.

So we can set or reset the memory, by applying logic 1 as an input signal to the set or reset connections. The memory then remains in this state when the input signal is removed. Note we never apply logic 1 to the reset and set connections at the same time!