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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.