Page 12 - DCAP206_INTRODUCTION_TO_COMPUTER_ORGANIZATION_AND_ARCHITECTURE_DCAP502_COMPUTER_ORGANIZATION_AND_ARCHITECTURE

Unit 1: Review of Basics of Digital Electronics

(b) ASCII Code: ASCII (American Standard Code for Information Interchange) has become Notes
a standard alphanumeric code for microcomputers and computers. It is a 7-bit code,
which represents 128 different characters. These 128 characters include 52 alphabets,
which include A to Z and a to z, numbers from 0 to 9 (that is, 10 numbers), 33 special
characters and symbols, and 33 control characters.
1.2 Logic Gates

A logic gate is an electronic device that makes logical decisions based on the different combinations
of digital signals available on its inputs. A digital logic gate can have more than one input signal
but has only one digital output signal.
Integrated Circuits or ICs can be grouped together into families according to the number of
transistors or gates. Integrated circuits are categorized according to the number of logic gates or
the circuit complexities within a chip.
AND Gate

AND gate is a type of digital logic gate, which has an output that is normally at logic level “0”
and goes “HIGH” to a logic level “1” when all of its inputs are at logic level “1”. The output of
AND gate returns “LOW” when any of its inputs are at a logic level “0”.

The Boolean expression for AND gate is Q= A.B.
A simple 2-input logic AND gate can be constructed using RTL structure connected together as
shown below in figure 1.2. Both transistors, T and T must be saturated “ON” to produce an output
1 2
at Q. In the figure 1.2, we can observe that the output from T is the input to T . Vcc is the input to
1 2
transistor 1 and the final output, Q=A.B, is obtained from T .
2
Figure 1.2: Design of AND Gate

LOVELY PROFESSIONAL UNIVERSITY 5