1. Embedded Systems Flashcards
What is an embedded electronic system?
An electronic system which improves the function of a product in some way but is not itself the primary purpose of the product.
What is an example of an embedded electronic system and why is it so?
E.g. a washing machine is an embedded system because almost every washing machine is controlled electronically by a micro controller (MCU or mC). This is an embedded system because the purpose of the product is to wash clothes, not computation.
Is a PC and embedded system and what does it contain?
A PC is not an embedded system because its main task is computation of some sort. But it does contain embedded systems e.g. the keyboard, disk drives etc.)
What are the names of the different approaches to implementing embedded systems?
- Discrete components
- Buy a computer
- Application specific integrated circuits (ASIC)
- Configurable hardware
- Microcontrollers
What are discrete components?
In the past, embedded systems would have been constructed from discrete components (transistors, resistors, etc) or small scale integrated circuits (7400 logic circuit). This approach is now largely obsolete.
What would s timer have been like in the past using discrete components?
Would have been made using a famous integrated circuit called the 555. It comes in an 8-pin package and costs 25p but needs several external components (resistors and capacitors).
Nowadays how would you make the timer?
You would buy a complete microcontroller in an 8-pin package for less than £1. This is more than the 555 but it does a better job and needs no external components.
Moreover, most microcontrollers include timers that run automatically in the background, leaving the computer free to carry out other tasks!
What are the advantages of the buying a computer approach?
- Standard hardware, no development needed.
- Operating system provides all basic services needed (contrast with microcontrollers where you must do everything).
- Wide range of application software available.
What are the disadvantages to the buying a computer approach?
- The computer tends to be large and uses lots of power.
- Unreliable operating system (windows) prone to crashes (couldn’t be used in critical applications).
- Not basically a ‘real time system’ (although versions are available).
What are application specific integrated circuits?
Basically custom made chips. For very large scale production or where highest performance is needed ASIC’s are used. These are very expensive to design (>$1mil in upfront costs) but fit most of the system on a single chip (IC) rather than needing a PCB with lots of IC’s.
What is configurable hardware?
The use of general purpose hardware that can be wired up to perform a given function. Typically contain a large array of logic gates and flip flops, whose connections can be programmed to give the desired operation. Examples include PLDS - programmable logic devices and FPGAs - field programmable gate arrays.
What is a hardware description language?
E.g. this logic circuit connects to this one.
What is the difference between configurable hardware and microcontrollers?
There is no clear cut distinction between this approach and microcontrollers. A FGPA can be programmed to act as a microcontroller.
What does the microcontroller approach involve?
A device with nearly fixed hardware but whose operation can be programmed in a versatile way.
What is a microcontroller?
Essentially a computer on a chip, Modern devices incorporate almost all of the functions that needed peripherals in the past.
