Historical Computer Engineering - Logical Circuits
Mode: Visitor // Expert
Language: Deutsch English

Logical Circuits

OR (Disjunction)

Get Adobe Flash Player

Introduction

The OR gate has two OR-combined input terminals.
If at least one of the input terminals is true, the output will also be true.
This means that the output Z will be HIGH (1), if input-terminal A or input-terminal B is HIGH (1). The output Z will also be HIGH (1), if both input-terminals are HIGH (1). Otherwise the output Z will be LOW (0).

Example

claim: Emilia works as a babysitter or at the till.
(If Emilia doesn't work, the claim will be false.)
If... the claim will be...
Emilia doesn't work, False
Emilia works as a babysitter, True
Emilia works at the till, True
Emilia works both as a babysitter and at the till, True

claim (Z) = Emilia works as a babysitter (A) or at the till (B).
A B Z
No babysitter No till girl False
No babysitter Till girl True
Babysitter No till girl True
Babysitter Till girl True

Z = Emilia works as a babysitter OR at the till.
1: Emilia has one or more jobs / true
0: Emilia doesn't work / false

Truth table

Z = A OR B
A B Z
0 0 0
0 1 1
1 0 1
1 1 1

Functional equation

Functional equation of OR

Electronic Symbol

symbol of the OR

Exercises

Propositional calculus with words:

claim: Tomorrow it will snow or it'll be warmer than 30 degrees.

If it won't snow tomorrow although it will be -2°C cold, the claim will be __________.
false
If it will be 36°C warm tomorrow, the claim will be __________.
true
If it will snow tomorrow and temperature will be 32°C, the claim will be __________.
true

Specials

It is possible to build this gate just from NAND gates:
A OR B = (A NAND A) NAND (B NAND B)
OR from NAND

CMOS implementation

Get Adobe Flash Player