CHAPTER 2
EMBEDDED SYSTEM
An embedded system is a special-purpose computer system designed performs one or a few dedicated functions, often with real-time computing constraint [2]. In general, embedded system means the processors is embedded into that application. The majority of computer system in use today is embedded in other machinery, such as telephones, clocks, applications and vehicles.
An embedded system may have minimal requirement for memory and program length. Input and output devices may be discrete switches, relays or solenoids. An embedded controller may lack human-readable interface devices. For example, embedded systems usually don’t have keyboards, screen, disks, printers or other recognizable I/O devices of a personal computer.
Microcontrollers may control electric motors, relays, voltages and many read switches, variable resistors and other electronic devices. An embedded product uses either a microcontroller or microprocessors to do one task at a time .in an embedded system, there is only one application software that is typically burned into ROM. Example, printer, keyboard, video game player, etc…
2.1. Characteristics
1. Embedded system is designed to do some specific task, rather than a general purpose computer for multiple tasks. Some also have real-time performance constraints that must be met, for reason such as safety and usability; others may have low or no performance requirement, allowing the system hardware to be simplified to reduce cost.
2. Embedded systems are not always separate devices [2]. Most often they are physically built-in to the devices they control.
3. The software written for the computer systems is often called firmware, and is stored in read-only memory or flash memory chips rather than disk drives. It often runs with limited computer hardware resources small or no keyboard, screen and little memory.
2.2. Real-Time Embedded Systems
In the simplest form, real-time systems can be defined as those systems that respond to external events in a timely fashion, the response time is guaranteed [4]. We revisit this definition after presenting some examples of real-time systems.
Fig 2.1: A simple view of real-time systems
External events can have synchronous or asynchronous characteristics. Responding to external events includes recognizing when an event occurs, performing the required processing as a result of the event, and outputting the necessary results within a given time constraint. Timing constraints include finish time, or both start time and finish time.
A good way to understand the relationship between real-time systems and embedded systems is to view them as two intersecting circles, as shown in. It can be seen tha0t not all embedded systems exhibit real-time behaviors nor are all real-time systems embedded. However, the two systems are not mutually exclusive, and the area in which they overlap creates the combination of systems known as real-time embedded systems.
Fig 2.2: Real-time embedded systems
Knowing this fact and because we have covered the various aspects of embedded systems in the previous sections, we can now focus our attention on real-time systems.
2.3. Peripherals
Embedded system talk with the outside world via peripherals, such as
· Serial communication interfaces (SCI): RS-232, RS-422, RS-485 etc.
· Synchronous serial communication interfaces: 12C, JTAG, SPI, SSC, AND ESSI.
· Universal serial bus(USB)
· Networks: Ethernet, Controller Area Network, LAN Works etc.
· Timers: PLL(s) capture/compare and Time Processing Units.
· Discrete I/O: General Purpose Input/output (GPIO).
. Analog to Digital/Digital to Analog (ADC/DAC).
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