Computer systems 3 IO/ embedded devices Flashcards
What are signals and what are they used for?
Signals are time-varying “quantities” which convey some sort of information. The quantity that’s time-varying is usually voltage (or current).
Signals are passed between devices in order to send and receive information, which might be video, audio, or some sort of encoded data.
Signals can be transmitted through wires or pass through the air via radio frequency (RF) waves.
Audio signals, for example, might be transferred between your computer’s audio card and speakers, while data signals might be passed through the air between a tablet and a WiFi router.
What is an analog signal and what are some inputs?
● Have any value within a certain range.
● Values continuously vary with time.
● Used to represent continuous data.
Analogue sensors: temperature sensor, PIR sensor, accelerometer, humidity, sound, light, CO2 or similar.
What is an digital signal and what are some inputs?
● Have two discrete values (1/0 or ON/OFF).
● In electrical circuits these states are represented by voltages (5V = ON and 0V = OFF).
Digital sensors: pushbutton, switch, keypad, keyboard.
Digital signals maintain their quality better than analogue signals.
What is noise
All signals become weaker as they travel long distances. They may also pick up random extra signals. This is called noise. It is heard as crackles and hiss on radio programmes. Noise affects both analogue and digital signals.
How does noise affect analogue signals
Noise adds extra random information to analogue signals. Each time the signal is amplified, the noise is also amplified. Gradually, the signal becomes less and less like the original signal.
How does noise affect digital signals
Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the amplitude of the ON states. As a result, the electronics in the amplifiers can ignore the noise and it does not get passed along. This means that the quality of the signal is maintained, which is one reason why television broadcasters have changed from analogue to digital and radio broadcasters are in the process of changing.
Digital signals can carry more information per second than analogue signals, higher quality programmes or more channels can be broadcast. Another advantage of digital signals is that information can be stored and processed by computers.
Define an embedded system and give examples
An embedded system is a small computer that forms part of a larger system, device or machine. Its purpose is to control the device and to allow a user to interact with it. They tend to have one, or a limited number of tasks that they can perform.
Defining characteristics of embedded systems:
1. Application specific - general programmed and optimized to run one specific application.
2. Do not always have a user interface - typically receive input from sensors or a connected data source instead of directly from the user.
3. Hardware and software - contains a software application to run a specific service, along with the necessary hardware to run the application.
Examples: central heating systems, engine management systems in vehicles, dishwashers, TVs, digital watches, electronic calculators, GPS systems, fitness trackers, micro:bits.
What are the advantages of embedded systems?
Cost - cheap to design and build.
Speed/efficiency - tend to require less power.
Automated - requires minimal user intervention
What are the disadvantages of embedded systems?
Usually only fit for one function.
Not programmable by a user.
Difficult to upgrade (although software updates can help).
What is real time computing?
Real-time computing describes the capability of a computing system to respond to a given input within a tightly constrained time frame. In the context of embedded systems, engineers implement real-time computing by installing a special type of operating system onto the embedded device. Operating systems can be conceptualized as the bridge between embedded hardware and software. There are two basic types for embedded engineers to choose from:
What is a general purpose operating system? (GPOS)
General Purpose Operating System (GPOS) - the software layer that sits between the hardware and the application in an embedded system. It supports process management, memory management, device drivers, timer service, interprocess communication, file system and user interface. A GPOS is used in cases where tasks are not time-sensitive and computing power is valued more highly than rapid response times. E.g general desktop or laptop computer.
What is a real time operating system (RTOS)?
Real-Time Operating System (RTOS) - are those that respond to some external stimuli within a stated/minimum time. An RTOS is used for embedded systems applications that are time-sensitive or time-critical. A time-critical task is defined as one where the task must be performed within specified time constraints to avoid negatively impacting users. E.g. Air bag deployment depends on the rapid response time of a real-time embedded system with Hard RTOS.
