Task 1
For each of the gates listed below, explain their operation showing appropriate gate symbols, truth tables and logic equations for the outputs in terms of the input variables.
a) Two input OR gate
Logic gates process signals which represent true or false. Normally the positive supply voltage +Vs represent true and 0V represents false. Other terms which are used for the true and false states are shown in the table on the right. It is best to be familiar with them all.
The output Q is true if input A OR input B is true (or both of them are true): Q = A OR B
An OR gate can have two or more inputs, its output is true if at least one input is true.
Input A
Input B
Output Q
0
0
0
0
0
Traditional symbol
IEC symbol
Truth Table
b) Two input AND gate
The AND gate is a digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output (1) results only if both the inputs to the AND gate are HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output results.
AND
INPUT
OUTPUT
A
B
A AND B
0
0
0
0
0
0
0
c) Two input NAND gate
NAND gates are one of the two basic logic gates (along with NOR gates) from which any other logic gates can be built. Due to this property, NAND and NOR gates are sometimes called "universal gates". However, contrary to popular belief, modern integrated circuits are not constructed exclusively from a single type of gate.
For each of the gates listed below, explain their operation showing appropriate gate symbols, truth tables and logic equations for the outputs in terms of the input variables.
a) Two input OR gate
Logic gates process signals which represent true or false. Normally the positive supply voltage +Vs represent true and 0V represents false. Other terms which are used for the true and false states are shown in the table on the right. It is best to be familiar with them all.
The output Q is true if input A OR input B is true (or both of them are true): Q = A OR B
An OR gate can have two or more inputs, its output is true if at least one input is true.
Input A
Input B
Output Q
0
0
0
0
0
Traditional symbol
IEC symbol
Truth Table
b) Two input AND gate
The AND gate is a digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output (1) results only if both the inputs to the AND gate are HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output results.
AND
INPUT
OUTPUT
A
B
A AND B
0
0
0
0
0
0
0
c) Two input NAND gate
NAND gates are one of the two basic logic gates (along with NOR gates) from which any other logic gates can be built. Due to this property, NAND and NOR gates are sometimes called "universal gates". However, contrary to popular belief, modern integrated circuits are not constructed exclusively from a single type of gate.
