Concepts of Engineering
and Technology
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Basic Electricity and
Electronics
Module Three
Microprocessor Basics
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An Inverter

Lets go back to our first transistor circuit:
VCC
RC
VI
VO
VI = 0, the transistor is
off, VO = VCC (+ 5 V)
VI = 1, the transistor is
on, VO = 0 (ground)
ground
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Copyright © Texas Education Agency, 2012. All rights reserved.
An Inverter
VCC
Don’t like the inverter? Here
is a circuit that does not invert
VI
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RE
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We have established the concept that
voltage turns on or off transistors
We use transistors to make the circuits
that do what we need
What circuit do we need to make a binary
adder?
First, let’s look at what the adder circuit
has to do:
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The OR gate

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When ANY input is high, the output goes
high
Does not perfectly match what we need,
but gives us a starting point
A
B
If EITHER input goes high,
the transistor turns on
This is called an OR gate
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
This circuit works better
A
B


The diodes protect one input from
the other
The resistor limits current
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Truth Table

The truth table for the OR gate:
A B Q
A
B

Q
0
0
1
1
0
1
0
1
(Or X)
0
1
1
1
Schematic
symbol
When ANY input is high, the output
is high
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The AND Gate

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When BOTH inputs are high, we produce a
carry
We need a circuit that will turn on only when
both inputs are on
VCC
A
0
0
1
1
B
0
1
0
1
Q
0
0
0
1
A
B
Q
RE
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Schematic
symbol
Schematic Symbols

We have seen the schematic symbols for 2
gates:
 AND
 OR

Here is the schematic symbol for the
inverter:
 NOT

With these three gates, you can make any
logic circuit
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Back to the Adder

Here is how we make a binary adder:
A
B

A B
Σ (sum)
0
0
CO (carry) 1
1
0
1
0
1
All circuits are made physically with
transistors, but represented by symbols
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Σ Co
0
1
1
0
0
0
0
1
Digital Logic

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Digital logic is used for circuit design
Also used for mathematical operations

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The English language use of the terms
“and,” “or,” “not” do not always have the
same meaning as the logical terms
There are 7 total logic gates

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Called “Boolean Algebra”
AND, OR, NOT, NAND, NOR, Exclusive-OR,
Exclusive-NOR
These gates are the building blocks for
computers
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Logic Circuit Applications

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A memory decoder
A memory address is a unique number
A 2-bit code unlocks one
of 4 memory locations
when D goes high
A 4-bit code would unlock
one of 16 memory
locations when D goes high

Most logic circuits are simple, as this
example shows
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3 Bit Decoder

Any 3 bit binary number enables one AND
gate
A0
A1
A2
D0 = 0 0 0
D1 = 0 0 1
D2 = 0 1 0
D3 = 0 1 1
D4 = 1 0 0
D5 = 1 0 1
D6 = 1 1 0
D7 = 1 1 1
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A3
A4
A5
A0
A1
A2
7
6
5
4
3
2
1
0
F
E
D
C
B
A
9
8
1
7
1
F
2
7
2
F
1
6
1
E
2
6
2
E
1
5
1
D
2
5
2
D
1
4
1
C
1
3
1
B
2
4
2
C
2
3
2
B
1
2
1
A
2
2
2
A
1
1
1
9
2
1
2
9
3
7
3
F
3
6
3
E
3
5
3
D
3
4
3
C
3
3
3
B
3
2
3
A
3
1
3
9
1
0
1
8
2
0
2
8
3
0
3
8
6 address lines, 16 AND gates and 6 inverters enable 64
memory locations
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Computer Basics
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A computer uses voltage on wires to
communicate
Communication involves data, addresses,
and instructions
Each of these are represented by binary
numbers in a code
A logic circuit similar to what we have just
seen is used to decode each of these
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A computer has several basic parts

The input unit

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The output unit
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Monitor, printer, modem
Memory


Keyboard, mouse, modem, transducer
RAM, hard drive, CD-ROM
CPU
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Central processing unit
Also called a microprocessor
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The CPU
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The CPU is also called the microprocessor
The brains of the computer
Performs arithmetic and logic

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Has an internal ALU
Works based on an internal program
called microcode
The primary job of a CPU is to execute
instructions
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Instructions

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Where do instructions come from?
Humans write programs
A program is made by a series of
instructions
Instructions are processed sequentially
Program instructions get decoded
An instruction set is used for a family of
microprocessors
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
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Most program instructions are simple:
load, store, move, add
The type of program a CPU
understands is called machine code
A higher level language like C or Java
is compiled or interpreted into
machine language
Each instruction the computer
understands is represented by a
binary number
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
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A logic circuit similar to what we have seen
decodes the instruction into a particular
sequence of internal operations
To decode CD audio, a program runs in the
computer
The program describes how to read the data
from the CD and what to do with the data
when it is read
The CD audio data is also a series of
numbers
Voltage on wires is used to represent the
numbers (data, instructions, and addresses)
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
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If you look at a motherboard, you
can see all the wires that are used to
communicate
Wires are grouped and separated by
function
A group of wires is called a BUS
For example, a 32 bit address bus is
a group of 32 wires that connects
chips


CPU to RAM
CPU to devices/expansion slots
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
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Addresses go on an address bus
Data goes on a data bus
On a motherboard, the two are
separate physically
Other buses are: the control bus and
the power bus
Program instructions are a form of
data
Data and program instructions are
sent at different times on the same
wires
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Examples of control signals

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Clock and timing signals
Memory read or write
Memory vs. other input/output types
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RAM vs keyboard/mouse
Ready to send/clear to send/interrupt
Enable/disable
These are all on/off, controlled by voltage
on a wire
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The Clock
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The clock does two basic things:
Tells when to start
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Like a starters pistol
Starts on an edge of the clock signal
Tells how long an operation lasts
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The duration
A half hour show vs. a one hour show
How long things take can determine clock
rates
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The Clock
The clock signal is used to synchronize all
microprocessor operations
Start of next cycle or process
Duration
Start
(One Clock Cycle)
Time Elapses
(Like ticks of a clock)
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CPU Block Diagram
Instruction
Register
Instruction
Decoder
Program
Counter
Input/
Output
Data
Bus
Data
Register
1001011101
10010111
Address
Bus
ALU
1001011101
Clock
Stack
Bus Controller
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Memory
Key Facts
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The data bus is bi-directional
The address bus is uni-directional
The program counter holds the address of
the next memory location to be used
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The next address is the last address + 1
The stack holds the addresses of programs
and data the CPU is not currently using
Internal registers form a queue of program
instructions and data
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A Program Example
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Lets go through an example of the steps a
CPU goes through to read CD data
A program is a series of instructions
A program loops over and over again
What is the program doing while it loops?
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Waiting for user input
Generating routine output
Handshaking with devices
 Video output

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Step One
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The address in the program counter gets put on
the address bus
This address is for a program instruction in RAM
A read control signal is placed on the control bus
The program instruction code from memory is
placed on the data bus
The program counter adds one to the old
address
The CPU reads the instruction and executes
whatever is necessary to perform the instruction
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Step 2
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The next address (which is the old address plus
1) gets placed on the address bus
A read control signal is placed on the control bus
The program instruction at that address is
placed on the data bus
The program counter adds one to the old
address
The CPU reads the instruction, decodes it, and
executes it
This instruction tells the CPU to read data from
the CD
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Step 3
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The address in the program counter is placed on
the stack
The CPU determines the next available free
memory location, and places that address in the
program counter
This address is placed on the address bus
A write control signal is placed on the control bus
The CD drive reads data off the CD disk and loads
the data into memory at the location in the PC
A one (1) is added to the address in the program
counter
The next piece of data is loaded into the next
memory location, etc.
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Next Steps

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When the CPU wants to go back to running the
program, the current data location is taken from
the program counter and placed on the stack,
the next program instruction is taken off the
stack and loaded back into the program counter
Data and program instruction memory locations
are stored on the stack
Only current program addresses (or data
locations) are in the program counter
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CD Data to Audio

A CD that can read data at 52X can read data
off the disk at 7.8 million bytes/sec
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CD audio data is recorded and reproduced at
exactly 176,400 bytes/sec
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1X is 150 KB/sec
44,100 samples/sec X 2 bytes/samples X 2 channels
Excess data is buffered in memory
Binary data is processed by converting each 16
bit number to a voltage with a signal amplitude
given by the data numerical value
The voltage is sent to the speaker, which
produces sound
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