LOGIC GATES WHAT ARE LOGIC GATES A logic

WHAT ARE LOGIC GATES? • A logic gate is a digital circuit which either

WHAT IS A TRUTH TABLE? • A Truth Table list down all possible input

NOT GATE Truth Table Inpu t A B Outpu t • A NOT gate

NOT GATE EXAMPLE Central Heating ON/OFF Temperature Detector (Above 20 C) If the temperature

OR GATE Truth Table A Input s C B • An OR gate has

OR GATE Front Doorbell Switch Back Doorbell Switch • If either the Front Doorbell

AND GATE Truth Table A Input s C B • An AND gate has

AND GATE Person Sensor Alarm Switch • If both the Person Sensor AND the

LOGIC CIRCUITS • A Logic Circuit consists of a number of logic gates which

LOGIC CIRCUITS Truth Table • Example of a simple Logic Circuit containing an OR

LOGIC CIRCUITS Truth Table • An example of a more complex Input Logic Circuit

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LOGIC GATES

WHAT ARE LOGIC GATES? • A logic gate is a digital circuit which either allows a signal to pass through it or to stop it. • A logic gate accepts input in Binary. • A logic gate can accept one of two different inputs. These are either: • • 1 (also known as high or on) 0 (also known as low or off)

WHAT IS A TRUTH TABLE? • A Truth Table list down all possible input combinations of a logic gate and also lists down the output. Input to Logic Gate Output A B C 0 0 1 1 1 0 1 1 Output of Logic Gate

NOT GATE Truth Table Inpu t A B Outpu t • A NOT gate has only 1 input. In this example it is called A. • A NOT gate is also known as an Inverter. This is because it reverses the given input. Input Output A B 0 1 1 0

NOT GATE EXAMPLE Central Heating ON/OFF Temperature Detector (Above 20 C) If the temperature is above 20 C then the Central Heating is switched off. If the temperature is below 20 C then the Central Heating is switched on.

OR GATE Truth Table A Input s C B • An OR gate has two inputs. • The output will be a 1 if at least one input is 1. Outpu t Input Output A B C 0 0 1 1 1 0 1 1

OR GATE Front Doorbell Switch Back Doorbell Switch • If either the Front Doorbell Switch OR the Back Doorbell Switch is pressed, then the doorbell rings. Ring the Doorbell

AND GATE Truth Table A Input s C B • An AND gate has two inputs. • The output will be a 1 if all inputs are 1. Outpu t Input Output A B C 0 0 1 1 1

AND GATE Person Sensor Alarm Switch • If both the Person Sensor AND the Alarm Switch are on the Burglar Alarm is activated. Ring the Burglar Alarm

LOGIC CIRCUITS • A Logic Circuit consists of a number of logic gates which perform logical operations on data. Example of a Logic Circuit containing two AND gates, two NOT gates and an OR GATE.

LOGIC CIRCUITS Truth Table • Example of a simple Logic Circuit containing an OR gate and a NOT gate. A Input C D B Output A B C D 0 0 0 1 1 0 1 0 1 1 1 0

LOGIC CIRCUITS Truth Table • An example of a more complex Input Logic Circuit containing AND, OR, NOT gates and 3 inputs. A D B F C E Output A B C D E F 0 0 1 0 1 1 1 0 0 1 1 1 1 1 0 0