Date post: | 30-Nov-2014 |
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Software Developers View of Hardware
Electronic Circuits
What are circuits?
Computers are electrical devices, so therefore all functions performed by a computer need to done via the use of circuits.
Circuits are designed via the use of Logic Gates which show the path and the way in which electronic signals are sent and received.
Logic Gates
Are a hardware circuit that produces a 0 or 1, which is normally an electronic impulse.
There are THREE basic logic gates and THREE extended gates that can be used to build integrated circuits.
BASIC GATES
1. NOT Gate This is the simplest of all gates, it involves a
single input and a single output. The purpose of this gate is the flipping of a bit
similar to what is performed in one’s complement.
NOT Gate
0 1A X
NOT Gate
NOT Gate
NOT Gate – Truth Table
A X
0 1
1 0
IF A = 0 THEN
X = 1
ELSE
X = 0
ENDIF
BASIC GATES
2. AND Gate This is involves two inputs to produce one
output. Both inputs must be true for the output to be true.
AND Gate
A
X
B
AND Gate
AND Gate
AND Gate
AND Gate – Truth Table
A B X
0 0 0
0 1 0
1 0 0
1 1 1
IF A=1 AND B=1THEN
X = 1
ELSE
X = 0
ENDIF
BASIC GATES
3. OR Gate This is involves two inputs to produce one
output. If either inputs are true then the output will be
true.
OR Gate
A
X
B
OR Gate
OR Gate
OR Gate
OR Gate
OR Gate – Truth Table
A B X
0 0 0
0 1 1
1 0 1
1 1 1
IF A=1 OR B=1THEN
X = 1
ELSE
X = 0
ENDIF
Activity 1
Complete the truth table for the following circuit.
A
B
YX
Truth Table
A B X Y
0 0
0 1
1 0
1 1
EXTENDED GATES
1. NAND Gate This is involves two inputs to produce one
output. The output is the opposite of an AND gate. Is a combination of an AND and NOT gate.
NAND Gate
A
X
B
NAND Gate – Truth Table
A B X
0 0 1
0 1 1
1 0 1
1 1 0
IF A=1 AND B=1THEN
X = 0
ELSE
X = 1
ENDIF
EXTENDED GATES
2. NOR Gate This is involves two inputs to produce one
output. The output is the opposite of an OR gate. It is a combination of an OR and NOT.
NOR Gate
A
X
B
NOR Gate – Truth Table
A B X
0 0 1
0 1 0
1 0 0
1 1 0
IF A=1 AND B=1THEN
X = 0
ELSE
X = 1
ENDIF
EXTENDED GATES
3. XOR Gate This stands for exclusive OR. This gate is true if only one input is true.
XOR Gate
A
X
B
XOR Gate – Truth Table
A B X
0 0 0
0 1 1
1 0 1
1 1 0
SPECIALITY CIRCUITS
Designed to make use of our binary knowledge and our circuitry knowledge
Examples include: Adders Flip Flops Shifts
DESIGNING SPECIALITY CIRCUITS
These circuits are written to provide a specific function: Adder (Binary Addition) Flip Flop (Binary Storage)
DESIGNING SPECIALITY CIRCUITS
Follow these steps: Identify inputs and outputs Identify the components required to produce the
output (AND, OR, NOT, NAND, NOR, XOR) Construct the solution with logic gates Check the solution for validity (with a truth table) Evaluate the circuit design (could you make this
circuit better by chaining different logic gates)
Binary Half Adder
This device is basically a calculator. Lets look at the half adder truth table first.
Binary Half Adders
To create a Binary Adder, we need to find a logic gate that give us the Carry output and a logic gate the Sum output
INPUT OUTPUT
A B Carry Sum
0 0 0 0
0 1 0 1
1 0 0 1
1 1 1 0
Binary Half Adders
Carry output is created using a
INPUT OUTPUT
A B Carry Sum
0 0 0 0
0 1 0 1
1 0 0 1
1 1 1 0
AND logic gate
AX
B
Binary Half Adders
Sum output is created using a
INPUT OUTPUT
A B Carry Sum
0 0 0 0
0 1 0 1
1 0 0 1
1 1 1 0
XOR logic gate
AX
B
The circuit:
Binary Half Adders
A
B
Carry (C)
Sum (S)
Half And Full Adders
Half Adders only work to add two digits To add more than 2 binary digits we need a full
adder A full adder allows us to add the “carry” value to
an binary addition
Full Adders
A
B
Carry (C)
Sum (S)
Carry in
Truth Tables
Construct a truth table for the full adder.
Truth Table
A B CARRY IN
CARRY SUM
0 0 0 0 0
0 0 1 0 1
0 1 0 0 1
0 1 1 1 0
1 0 0 0 1
1 0 1 1 0
1 1 0 1 0
1 1 1 1 1
Circuit Design Steps
Identify inputs and outputs.
A + B + C = X Identify the components needed to obtain
the desired output.
AND/OR/NOT/XOR/NAND/NOR Construct a truth table to test.
Activity 2
Construct a truth table for the following circuit.
YAB X
C
A B C Y X0 0 0 1 10 0 1 1 00 1 0 1 10 1 1 1 01 0 0 1 11 0 1 1 01 1 0 0 01 1 1 0 1
AB X
C
Activity 3
Fault Door Switch x Light0 0 0 00 0 1 00 1 0 00 1 1 11 0 0 01 0 1 01 1 0 01 1 1 0