Everything Science Grade 12

14.5 CHAPTER 14. ELECTRONICS

A B C Output

0 0 1 0

0 1 0 1

1 0 0 1

1 1 0 1

Finally we see that this combination of gates does the same job as an ORgate.

Each logic gate is manufactured from two or more transistors. Other circuits can be
made using logic gates,as we shall see in the next section. We shall show you how
to count and store numbers using logic gates.This means that if youhave enough
transistors, and you connect them correctly to make the right logic gates,you can make
circuits which count andstore numbers.

In practise, the cheapest gate to manufacture isusually the NAND gate. Additionally,
Charles Peirce showedthat NAND gates alone(as well as NOR gatesalone) can be
used to reproduce all the other logic gates.

Exercise 14 - 7

1. Why is digital electronics important to modern technology and information pro-
   cessing?


2. What two symbols are used in digital electronics, to represent a “high” and a
   “low”? What is this system known as?


3. What is a logic gate?


4. What are the five main types of logic gates? Draw the symbol for eachlogic gate.


5. Write out the truth tables for each of the fivelogic gates.


6. Write out the truth table for the following circuit. Which single gate isthis circuit
   equivalent to?


7. Write out the truth table for the following circuit. Which single gate isthis circuit
   equivalent to?