MCT Chapter2

7/27/2019 MCT Chapter2

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Chapter 2:

Introduction to Microprocessor-

Based Control

Adapted from:

Kilian, C. T. (2001), Modern Control Technology: Components and Systems

Delmar


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Objectives

Understand what a microprocessor is, what it does, and

how it works.

Understand the concepts of RAM and ROM computer

memory and how memory is accessed via the address and

data buses.

Understand how parallel and serial data interfaces work.

Perform relevant calculations pertaining to analog-to-digital

converters and digital-to-analog converters.

Understand the principles of digital controller software.

Recognize and describe the characteristics of the varioustypes of available digital controllers, that is,

microcontrollers, single-board computers, programmable

logic controllers, and personal computers.


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Introduction

Microprocessors ushered in a whole new era

for control systems electronics.Microprocessors require additional

components to be useful RAM, ROM, etc.


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Microcontrollers are essentially

microprocessors with built-in features to beused independently.


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Reasons for Microprocessor Control

Low-level signals converted to digital can be

transmitted long distances error free.Micro can handle complex calculations.

Memory is available for tracking and storage.

Loading new programs for control change iseasy.

Easily connected to networks.


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A computer is made up of four basic blocks:

Central Processing Unit (CPU) Does the actual computing.

Arithmetic Unit performs math and logic

Control: Manages flow of data Memory Data is contained in memory

locations at specified addresses.

RAM volatile, read/write memory

ROM nonvolatile, read only

EPROM/EEPROM/Flash Erasable ROM


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Input/Output ports: Used for connections to

devices.Busing:

Devices are multiplexed using 3 major buses:

Address Bus To specify the device or memorylocation to communicate with.

Data Bus To transfer data between the CPU and

device.

Control Bus Timing and event control, such as readand write operations.


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Microprocessor Instructions & Op-Codes

Each processor has its own instruction set

of commands to control its operation. Move data

Perform math operations

Perform logical operationsEach instruction has a unique Op-code, a

binary value associated to it.

01001101 or 4Dh.An Accumulatoris staging area for data

data is moved into it, and operations are

performed on that data.


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INTERFACING TO A

MICROPROCESSOR

CONTROLLER

Parallel Interfacing

Serial Interfacing


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Parallel Interfacing

transfers data 8 bits (or more) at the same

time, using eight separate wires.ideal for inputting or outputting data from

devices that are either on or off.

For example, a single limit switch uses onlyone input bit, and an on-off signal to a motor

requires only one output bit.

These 1-bit signals are called logic variables,and eight such signals can be provided from

a single (8-bit) port.


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DAC

Driving a variable-speed DC motor - DAC

Digital-to-Analog Converter (DAC) converts8-digital data to analog voltage.


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DAC Formula & Resolution

Vout = Input x Vref

256 (for 8-bit)Vout = DAC output analog voltage

Input = Decimal value of binary input

Vref= Reference DC voltage


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ResolutionThe worst case error introduced when

converting.In an 8-bit DAC, there are 255 possible

steps. The resolution is the smallest step

size, or 1/255, 0.39%.In an 16-bit DAC, there are 65,535 possible

steps. The resolution is the smallest step

size, or 1/65535, 0.0015%.


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A DAC has a 5V reference with a binary

input of 10010100, calculate the voltageoutput.

If the binary input were 11111111?


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ADC

Analog-to-Digital converter (ADC):

A circuit that converts an analog voltage todigital word.


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ADC

Conversion Time: The time required to

convert an analog voltage to digital.

For an 8-bit ADC:

Output = Vin x 255Vref


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Serial Interface

Data is sent 1 bit at a time.

Reduces number of cables or lines More easily shielded from noise.

Existing data lines may be used (phone).

Parallel data must be converted to serial totransmit, and vice-versa on receive.

A UART (Universal Asynchronous Receiver

Transmitter) is a device which performs this

conversion.


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Asynchronous Transmission

Data is sent with defined timing, termed a

BAUD rate. 2400bps,9600, 19200, etc. StartBit & Stop Bit are used to frame the signal.

A parity bit is used optionally for error

detection.Common settings: 9600 Baud, 8 bits, no

parity, 1 stop-bit -- 9600 8-N-1

RS 232


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RS-232

RS-232 is a specification which defines

standard for serial interfaces between DTEs(Data Terminal Equipment Computers),

and DCEs (Data Communication Equipment

Modems, etc).

DTE to DTE communications can be

performed serially using a cross-over or Null-

Modem cable.


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N t ki


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Networking

Multiple devices are connected together.

Serial data is passed between devices.Devices are provided individual address

numbers to send data to a particular device.

C t ll P


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Controller Programmer

Real Time control

Program runs in a loop,sensing the current

condition and

calculating new output

to the actuator.

Each pass through the

program is an iteration

orscan.


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The frequency at which new data is collected

is the sampling rate (scan time).Time-delay loops may be inserted to slow

the execution or scan time.

Programs can be written at the lowest level(machine code, assembler) or high level

languages (C), BASIC, etc.

Mi t ll


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Microcontrollers

A single-chip computer specifically designed

for I/O control.On board RAM, ROM, possibly timers and

ADCs.

High speed is not required due to lowcomplexity of tasks.

Very large cost savings over

microcomputers.Motorola 68HC11, Intel 8051, PIC 16C72,

Atmel AVR, BASIC Stamp


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BASIC Stamp

Single Board Computers


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Single-Board Computers

A computer on a single board.

Programmable for I/O control and the abilityto use high level peripherals.

Programmable Logic Controllers


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Programmable Logic Controllers

Self-contained microprocessor based controller.

Designed for fast connection and control ofprocesses.

Used extensively in industrial control

environments.

Programs in relay-logic to be compatible to the

more traditional electrical workforce.

Personal Computers


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Personal Computers

PCs with dedicated I/O and data acquisition

cards and specialized software may be usedas controllers.


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The smallest step change in voltage for a

DAC or ADC is the voltage resolution howclosely a voltage can be resolved due to the

digital quantization:

With a 5V reference,1 LSB = 5V/255 = 19.5mV

(5V x .39% = .00195V)

ADCs and DACs have a resolution error of LSB.

LSB = 9.7 mV

In a ADC, the input voltage could be +/- 9.7mV.


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Given a 10-Bit ADC with a 5V reference,

calculate: The % Resolution

The LSB Value (volts)

The LSB Value (volts) The digital output for an input of voltage of 3.2V

Objectives Review


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Objectives Review

Understand what a microprocessor is, what it does, and

how it works.

Understand the concepts of RAM and ROM computer

memory and how memory is accessed via the address and

data buses.

Understand how parallel and serial data interfaces work.

Perform relevant calculations pertaining to analog-to-digital

converters and digital-to-analog converters.

Understand the principles of digital controller software.

Recognize and describe the characteristics of the various

types of available digital controllers, that is,

microcontrollers, single-board computers, programmable

logic controllers, and personal computers.

Documents

MCT Chapter2