University College Cork IRELAND Number Systems, Data Types, Codes Logic Gates: An Introduction

University College Cork IRELAND Number Systems Base Digit values Positional values -- integer powers of base Zero (0) to represent nothing in a given position Value of number = sum of products of digits and their positional values

University College Cork IRELAND Computer Number Systems

University College Cork IRELAND Octal and Binary Digits

University College Cork IRELAND Hexadecimal and Binary Digits

University College Cork IRELAND Data Types Numeric data –binary integer –floating-point –decimal value String data –a.k.a. character data –one character per byte –8-bit code such as ASCII or EBCDIC

University College Cork IRELAND ASCII and EBCDIC Codes.

University College Cork IRELAND Logic Gates Electronic circuits which combine digital signals according to the Boolean algebra are referred to as logic gates Gates because they control the flow of information. Positive logic is an electronic representation in which the true state (1) is at a higher voltage, while negative logic has the true state (0) at a lower voltage.

University College Cork IRELAND Logic Circuit Families Logic circuits are grouped into families, each with their own set of detailed operating rules. Some common logic families are: –RTL: resistor-transistor logic, –DTL: diode-transistor logic, –TTL: transistor-transistor logic, TTL is normally used for small-scale integrated circuit units –NMOS: N-channel metal-oxide silicon, MOS features very low power consumption and is used in VLSI technology –CMOS: complementary metal-oxide silicon and –ECL: emitter-coupled logic. ECL is very fast The. The TTL is normally used for small-scale integrated circuit units

University College Cork IRELAND Logic Gate Building Blocks Symbols and truth tables for the four basic two- input gates: a) AND, b) NAND, c) OR, d) NOR and e) the inverter. –The open circle is used to indicate the NOT or negation function and can be replaced by an inverter in any circuit. –A signal is negated if it passes through the circle. –Any logic operation can be formed from NAND or NOR gates or a combination of both. We also commonly have gates with more than two inputs. –Inverter gates can be formed by applying the same logic signal to both inputs of an NOR or NAND gate.

University College Cork IRELAND Examples of Logic Gates