EC01 Informatica Intro

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Informtica

Ing. Aeronutica

Introduction

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Ing. AeronuticaIntroduction

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Ing. AeronuticaSystems

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A black box is an object which interacts with the environment through itsinterface: inputs and outputs

The implementationor internals of a black box are opaque (black).

We are interested in whatit does rather than in howit does it: its functionality.

Abstraction is a process that allows to suppress all unneeded details from anobject and to retain only information which is relevant for a particular purpose.

- Black boxes are a way of abstracting a real system.

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A vending machine

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A systemdenotes a compound entity: it is a black box whose implementation isa set of interacting or interdependent systems and relationships betweensystems (recursive definition).

System composition: ability to interact and to combine with other systems inorder to configure a more complex system.

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Very important to distinguish between its specificationand its implementation.

- Specification:defines its interface and its functionality. It includes the definition

of all the inputs and outputs an their types.

- Implementation: defines its components and the system structure. It is not

unique.

System validationand certification.

- Validation: checking that a particular implementation meets the system

specifications. It usually refers to thecorrectnessin terms of functionality.

- Certification: checking that it not only meets the correctness specifications,

but also some additionalperformance, qualityorsafetyrequirements.! Certification procedures and standards for Avionics.

! DO-178B: Software Considerations in Airborne Systems and Equipment

Certification.

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Continuous-time system: inputs and outputs are defined over a time domainwhich is continuous. Example: T=[0,5]

Discrete-time system: the time domain is a discrete set of values. ExampleT= {0,1,2,3,4,5}. Inputs are only sampled at time instants in the domain andoutputs are reevaluated each time the inputs are sampled.

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Y(t) = adder(2,t)Continuous-time Discrete-time

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Combinational systems can be mapped to Matlab functions.

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Informtica

Ing. AeronuticaDigital systems

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Based onpredicates: sentences that assert or deny unambiguously an attribute.Example:Mary is wearing a flower on her head (true/ false)

Boolean domainB={0, 1}, 0"false, 1"true.

Operators:

- AND: x !y- true if both x and y are true and false otherwise.

! Example: The machine starts working if The green light is on " The button is

pushed.

- OR: x #y- true if either x or y are true and false otherwise.

! Example: The machine stops working if The button is pushed $ There is an

emergency.

- NOT:x- true if x is false and false if x is true

! Example: The machine is working if The red light is on %The red light is off.

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Laws similar to ordinary algebra:

- Commutativity of$and": x$y=y$x, x"y=y"x

- Associativity of$and": x$(y$z) = (x$y)$z x"(y"z) = (x"y)"z

- Distributivity: x$(y"z) = (x$y)"(x$z) x"(y$z) = (x"y)$(x"z)

Additional laws:

- Idempotence of$and": x$x=x x"x=x

- Absorption 1 and 2: x$(x"y) = x x"(x$y) = x

- De Morgan 1 and 2: (x"y) = x!$y! (x$y) = x!"y

- Opposites: x $x!!= 1 x "x!!= 0

- Neutral elements: x $0 = x x "1 = x

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Laws similar to ordinary algebra:

- Commutativity of+ and: x+y=y+x, xy=yx

- Associativity of+ and: x+(y+z) = (x+y)+z x(yz) = (xy)z

- Distributivity: x+(yz) = (x+y)(x+z) x(y+z) = (xy)+(xz)

Additional laws:

- Idempotence of+ and: x+x=x x x=x

- Absorption 1 and 2: x+(xy) = x x(x+y) = x

- De Morgan 1 and 2: (xy) = x!+ y! (x+y) = x! y

- Opposites: x + x!!= 1 x x!!= 0- Neutral elements: x + 0 = x x 1 = x

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Additional gates

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Function of the formf: Bn"B, B={0, 1}

- f(x1,x2,...,xn), where xiare Boolean variables.

They can be represented using expressionsor truth tables.

Shannon Expansion Theorem: A boolean function can be expanded in two

canonical forms: sum of mintermsand product of maxterms.

- Example: majority voting of three binary juries

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Expression could be simplified before implementing it.

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Matlab has a data type called logicalto support Boolean variables.

Logical operators:

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Ing. AeronuticaComputers

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A computer is a programmable machine designed to solve a given problemautomatically by executing a sequence of instructions (program).

- Hardware: physical system that implements the computer. The fixed parts that

make up a computer. Currently based on digital systems (combinational and

sequential circuits).

- Software: programs or list of instructions to solve a problem. They can be

changed readily, allowing the computer to solve more than one kind of problem.

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Its physical structure (hardware) is generic: it has not been designed to solve a

particular problem, but a wide range of problems.- This is what makes a computer different to most of other machines like an

engine or a screwdriver...

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System which takes information, processes it and provides the processed informationat the output.

- The program specifies how information is processed.

- Information needs to be encodedto the computer format.

Computer peripherals:allows interaction with the environment.

- Device attached to computer that expands the computer capabilities by allowing it to

take information in/out from/to the environment.

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A computer is a complex system made up of lots of subsystems.

Main computer subsystems are studied in chapter 3: Arithmetic-Logic Unit(ALU), Control Unit (CU), Memory, ... All these subsystems are, in turn, madeup of digital systems:

- Combinational circuits.- Sequential circuits.

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General purpose computers: they usually interact with human users and execute alarge variety of programs.

- Wide functionality.

- Examples: desktops, laptops, servers, etc.

Embedded systems:computers specialized in a specific task. They often interact witha machine (vehicle, engines, ...). Their goal is usually to take control or guidanceover a machine. Also most computer-based electronic appliances.

- Reduced functionality.

- Very specialized input and output devices calledsensorsandactuators.

! Sensor: device that measures a physical quantity and converts it into an electrical signal

or a computer code.

! Actuator: mechanism by which a computer acts upon the environment by transforming

an electrical signal or a computer output into some kind of motion.

- Examples 1:machine controllers, onboard computers, autopilots, vending machines,

- Examples 2: mobile phones, smart TV set.

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Inertial Measurement Unit (IMU): it computes the aircraft attitude that definethe aircraft orientation: roll, pitchand yaw.

- Based oninertial sensors (also available in most mobile phones): They detect

motion: three-axis accelerometer, gyroscope and compass to detect the

geomagnetic field.

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An FMS is a specialized computersystem that automates a widevariety of in-flight tasks, especiallynavigation guidance.

- The pilot programs the flight plan.

- The FMC guides navigation using:

! A navigation database

! Data from navaids, GPS and

other sensors.

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System that replaces the conventional mechanical flight controls of an aircraft withelectronic devices.

- The movements of flight controls (yoke, pedals) and sensors (accelerometers,

gyroscopes, Pitot tubes, etc.) are converted to electronic signals.

- Signals are transmitted between the aircraft subsystems through wires.

- Signals feed a computer called the Flight Control System (FCS) which computes

the control actions and sends them to the control surfaces (ailerons, elevators, flaps,

etc.) and to the engines using more wires.

Redundancy: most elements have a back-up to improve reliability.

Advantagesof FBW over mechanical and hydro-mechanical flight control systems:

- Lighter than mechanical systems, so they save weight.

- Easier routing through the aircraft.

- Much more flexible control.

Disadvantage:

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Examples of digital systems in avionics

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Landing gear door warning logic.- There are five switches that detect whether or not the respective landing gear door is open.

- There are five warning indicatros in the central panel that which door(s) are open.

- There is a master indicator in the pilots panel that provides a warning if some of the doors is open.

- A switch is also provided in order to enable or disable the five door warning indicators.

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Normal flight state

- All doors are closed

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Warning state

- Nose door open

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Warning state

- Nose and left wing doors open

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EC01 Informatica Intro