16-02-2013, 10:43 AM
Number Systems, Data Types, Codes Logic Gates: An Introduction
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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
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.
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
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.