TABLE OF CONTENTS A logic gate is an electronic circuit which makes logic decisions. It has one output and one or more inputs. The output signal appears only for certain combinations of input signals. Logic gates are the basic building blocks from which most of the digital systems are built up. They implement the hardware logic function based on the logical algebra developed by George Boole which is called Boolean algebra in his honor. A unique characteristic of Boolean algebra is that variables used in it can assume only one of the two values i.e., either 0 or 1. Hence, every variable is either a 0 or a 1.
These gates are available today in the form of various IC families. The most popular families are: transistor-transistor logic (TTL), emitter-coupled logic (ECL), metal-oxide-semiconductor (MOS) and complementary metal-oxide-semiconductor (CMOS).
In this chapter, we will consider the OR, AND, NOT, NOR, NAND and exclusive OR (XOR) gates along with their truth tables.
In computing systems, the number symbols 0 and 1 represent two possible states of a circuit or device. It makes no difference if these two states are referred to as ON and OFF, CLOSED and OPEN, HIGH and LOW, PLUS and MINUS or TRUE and FALSE. The main point is that they must be symbolized by two opposite conditions.
In positive logic, a 1 represents
an ON circuit
a CLOSED switch
a HIGH voltage
a PLUS sign
a TRUE statement.
Consequently,...
