DIGITAL LOGIC

1.5 DIGITAL LOGIC

Electronic digital computers are made of two basic kinds of compo¬nents: logic elements (often called switching elements) and memory elements. In virtually all modern computers these elements are binary, that is, the logic elements have two alternative pathways and the memory elements have two states. Accordingly all the information handled by such computers is coded in binary form. In short, the information is represented by binary symbols, stored insets of binary memory elements and processed by binary switching elements.

To make a digital computer, it is necessary to have memory elements and a set of logic elements. Let us examine a set of logic ele¬ments that contains three distinct types of circuits designated AND, OR and NOT. Such circuits can be depicted with input signals at the left and output signals at the right. Since the logic ele¬ments are binary, each input and output is a binary variable that can have the value 0 or 1.

Solid state electronic components are used to construct these and memory elements. In an electrical circuit the logical value 0 can for example correspond to a particular voltage or current and the logical value 1 to another voltage or current, or a logical value of 0 for off and 1 on. Shown below are examples of the ways binary logic can be used.