Section 2: Combinational Logic
(Reading: Wakerly Chapter 3 & Morris Mano)
University of KwaZulu-Natal 3-1
ENEL2EBH2 2010
, Digital Circuits
• Digital circuits can be described in terms of
combinational logic or sequential logic or
both. In a combinational logic, the output of a
digital circuit at any given instant of time is
completely determined by the inputs present
at that particular time. Examples of
combinational circuits include logic gates,
NAND gate, NOT gate, NOR gate and so
forth.
• In this section, we will consider combinational
circuits only.
University of KwaZulu-Natal 3-2
ENEL2EBH2 2010
, Truth Tables
A digital circuit can be thought of as a black box with inputs
and outputs.
A truth table is a list of all possible circuit inputs and
outputs.
Example: Passage or staircase light switch control:
INPUTS OUTPUTS
A B Y
0 0 0
0 1 1
1 0 1
1 1 0
University of KwaZulu-Natal 3
3-3
ENEL2EBH2 2010
(Reading: Wakerly Chapter 3 & Morris Mano)
University of KwaZulu-Natal 3-1
ENEL2EBH2 2010
, Digital Circuits
• Digital circuits can be described in terms of
combinational logic or sequential logic or
both. In a combinational logic, the output of a
digital circuit at any given instant of time is
completely determined by the inputs present
at that particular time. Examples of
combinational circuits include logic gates,
NAND gate, NOT gate, NOR gate and so
forth.
• In this section, we will consider combinational
circuits only.
University of KwaZulu-Natal 3-2
ENEL2EBH2 2010
, Truth Tables
A digital circuit can be thought of as a black box with inputs
and outputs.
A truth table is a list of all possible circuit inputs and
outputs.
Example: Passage or staircase light switch control:
INPUTS OUTPUTS
A B Y
0 0 0
0 1 1
1 0 1
1 1 0
University of KwaZulu-Natal 3
3-3
ENEL2EBH2 2010
