Lecture 2 MicrocontrollerLec2

8/9/2019 Lecture 2 MicrocontrollerLec2

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Lecture 2Microcontroller Introduction

Shaharyar Mahmood


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Microprocessor and Interfacing 2

So what exactly is a Microcontroller

Entire computer system contained within a

single integrated circuit.

The goal is to choose the most economicalMC that has the desired parameters and

features for the application at hand.


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Block Diagram


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Basic Architecture

CPU is a complex sequential circuit whoseprimary function is to execute programs that arestored within its Flash EEPROM.

A program is a series of instructions to perform aspecific task.

Program is developed on PC and downloadedinto the MC and MC becomes stand-aloneprocessing system.

Fetch-Decode-Execute cycle. CPU is the maincontrol center for the entire MC. CPU ismanaging program execution andcommunication with different subsystems.


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Software Development Process


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CPU Architectures


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RISC versus CISC

There are two basic types of instruction setarchitectures: Reduced Instruction Set Computer(RISC) and Complex Instruction Set Computer(CISC) Architecture.

In RISC architecture complex instructions arebuilt up from basic building block instructions.

RISC-based instruction architectures lendthemselves to systems with less complex CPU

architectures.A CISC-based architecture has a complement of

fuller feature, more complex instructions than theRISC-based architecture.


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Little-endian vs Big-endian

Endianness has to dowith the byte orderingof multibyte scalar

values. Suppose we have the

32-bit hexadecimalvalue 12345678 andthat it is stored in a32-bit word in byteaddressable memoryat byte location 184.

Address Value Address Value

184 12 184 78

185 34 185 56

186 56 186 34

187 78 187 12

Big Endian Small Endian


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Register Set

Usually all registers associated with a given subsystem are grouped together.


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Register Set

The register set is the interface between you the userand the different subsystems aboard the microcontroller.

Each register consists of a collection of flip-flops.

to set a register called SCI BaudRate to the binary value1010 1110:

SCI BaudRate = 0xAE;

Header files contain the personality data for a givenmicrocontroller.

Specifically, they provide a link between the name of aspecific register used within a program and its locationwithin the microcontroller.


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Bus Structure

A bus is a collection

of parallel conductors

that have a similar

function. Most MCsare equipped with an

address bus, a data

bus, and a control

bus.


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Address Bus

The address bus provides a connection between

the central processing unit and the memory

subsystem aboard the microcontroller.

The number of individually addressable memory

addresses may be determined by evaluating

(2)address lines =addressable locations. E.g. 16 bits

= 65536 (64kB). The first address in this

memory space is (0000)16 while the last addressin this space will be (FFFF)16.


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Data Bus

Used to route parallel data about different

subsystems within the MC. E.g. 4, 8, 16 or

32 bit.The width determines the size of a data

argument that the MC can process.

For example, the largest unsigned integer

that may be stored in a microcontroller

with an eight-bit data path is 255. (2^n)-1.


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Control Bus

Microcontrollers are equipped with paths to sendand receive a collection of control signalsdesignated as the control bus.

These signal lines carry control signals todifferent subsystems throughout themicrocontroller.

Some control signals are provided on ports toconnect external components.

Control signals are issued by the CPU inresponse to program instructions to ensure theinstruction is properly executed.


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Memory

The span of addressable memory usually

contains several different types of memory

including Static Random Access Memory

(SRAM), byte-addressable Electrically

Erasable Programmable Read Only

Memory (EEPROM), and bulk

programmable Flash EEPROM.


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Memory Map


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RAM

RAM is volatile. That is, if the microcontrollerloses power, the contents of RAM are lost.

It can be written to and read from duringprogram execution.

It is typically used during system development tostore a program. Once development is complete,the completed program is stored in nonvolatilememory such as Flash EEPROM.

Used to store global variables, support dynamicmemory allocation of variables, and to provide alocation for the stack.


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Byte-addressable EEPROM

This type of memory is used to

permanently store and recall variables

during program execution.

Used for logging critical data and to store

useful information during a power failure.

Applications include electronic lock

combinations, and automatic garage door

electronic unlock sequences.


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Flash EEPROM

Bulk programmable Flash EEPROM isused to store programs.

Flash EEPROM is typically programmedusing In System Programming (ISP)techniques. That is, a host PC isconnected via a cable to a microcontrollerwhile it is resident within its applicationcircuit. The host PC downloads theprogram to the microcontroller.


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AVR ISP


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TIME BASE

The speed at which a microcontroller

sequences through its actions is controlled

by an external time base.

The time base may be provided by an

external quartz crystal, a programmable

oscillator, a ceramic resonator, or an

internal time base.


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Timing Concepts

Frequency:Signal frequency is the number ofcycles per second completed by a repetitivesignal. It is expressed in units of Hertz (Hz).

Period:The period is the time increment inseconds required for a repetitive signal tocomplete a single cycle. The period is thereciprocal of the frequency (T= 1/ f).

Duty cycle:The duty cycle indicates thepercentage of time for which the signal is activein a single period.

Pulse width modulation (PWM):PWM signals arefrequently used to control motor speed.


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Timing Concepts


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Timing Subsystem Applications

Most microcontrollers are equipped with a multichannel timing system. The channels within thetiming system may be configured to:

Measure parameters of input signals such asperiod and duty cycle.

Generate precision output pulses or repetitivesignals.

Count incoming pulses present in an inputsignal.

Generate PWM signals.


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Port Systems

Ports provide access toexternal world.

8-bit ports along with data-direction registers.

Some ports have alternate

functions such as alternatefunctions such as analog-to-digital conversion, serialcommunication, and networkinterfacing.

Some have multiplexedcapability such as expansion

ports provided to routethe data and address portsoutside the microcontrollermay employ time multiplexedfeatures.


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Communication Systems

parallel communication techniques are

used for short distance communication

within and outside of a microcontroller.

For a long distance communication, a

serial communication technique is used to

send and receive data.


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Serial Communications

Synchronous and Asynchronouscommunication.

The asynchronous communication method usesa start and stop bit protocol to synchronize atransmitter and receiver.

Inexpensive, but the disadvantage is that thedata transmission rates are typically slower thana synchronous serial communication system dueto its overhead (start and stop bits).

Referred as UART (universal asynchronousreceiver transmitter) or the SCI (serialcommunications interface).


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Continued

The synchronous serial communication

uses a synchronized clock to send and

receive each bit.

For a long distance communication, the

synchronous serial communication

technique is not recommended.


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Terminology

Simplex mode: In this mode, the serialcommunication is accomplished by transmittingdata in one direction at a time.

Duplex mode: In this serial communicationmode, data can be transmitted and receivedfrom both ends of the communication link at thesame time.

BAUD rate: The rate of bits sent or received. Itdescribes the number of bits communicated persecond.


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Terminology Continued

ASCII code: The American Standard Code forInformation Interchange code is used incommunication to encode alphabets, numbers,

punctuation, and control characters using aseven-bit representation. ASCII is a subset ofthe international Unicode standard.

Bit time: The time required to transmit or receivea single bit.

Serial line code:A specific encoding mechanismused to transmit and receive information.


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RS-232 Protocol

The RS-232 standard represents a logic

high with a 10 VDC level and a logic low

with a +10 VDC level.

These chips are equipped to provide

interfacing for a two way (transmit and

receive) communication system.


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Interrupt System


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Speed

Microcontrollers are available in a wide range ofoperating speeds.

In general, you should use the lowest

acceptable speed for a given application. This is because that the power consumption of a

microcontroller is directly proportional to itsoperational speed. Since many microcontrollerapplications are battery powered, conservingpower and hence extending battery life isessential.


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ANALOG-TO-DIGITAL CONVERTER

This subsystem converts continuouslyvarying analog signals from the outsideworld into a binary representation suitable

for use by the microcontroller.These converters commonly have 810-bit

resolution.

Therefore, a continuous signal isconverted to a series of digital snapshotsof the analog signal.


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CHOOSING A MICROCONTROLLER FOR A

SPECIFIC DESIGN


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The End

Lecture 2 MicrocontrollerLec2

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