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THE TYPICAL EMBEDDED SYSTEM �UNIT 2 PREPARED BY PRIYANKA Y

  • CORE OF THE EMBEDDED SYSTEM
  • MEMORY
  • SENSORS AND ACTUATORS
  • COMMUNICATION INTERFACE
  • EMBEDDED FIRMWARE
  • OTHER SYSTEM COMPONENTS
  • PCB AND PASSIVE COMPONENTS

PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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OBJECTIVES :

After reading this chapter the student will be able to:

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  • Understand the different types of core i.e processor
  • Understand difference between microprocessor & microcontroller
  • Understand the classification of processors based on Bus
  • Architecture, Instruction set Architecture and Endianness.
  • Have an overview of processors from most simple and
  • cheap to most expensive and complex, powerful
  • Understand what are sensors and actuators, communication interfaces

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CORE OF EMBEDDED SYSTEMS�

Embedded systems are domain and application specific and are built around a central core. The core of the embedded system falls into any of the following categories:

General purpose and Domain SpecificProcessors

  • Microprocessors
  • Microcontrollers
  • Digital Signal Processors

Application Specific Integrated Circuits.(ASIC)

Programmable logic devices(PLD’s)

Commercial off the shelf components(COTs)

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GENERAL PURPOSE AND DOMAIN SPECIFIC PROCESSOR.�

  • Almost 80% of the embedded systems are processor/ controller based.

The processor may be microprocessor or a microcontroller or digital signal processor, depending on the domain and application.

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MICROPROCESSORS

�A microprocessor is a silicon chip representing a central processing unit.

  • A microprocessor is a dependent unit and it requires the combination of other hardware like memory, timer unit, and interrupt controller, etc. for proper functioning.
  • �Architectures used for processor design are Harvard or Von Neumann.

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Endianness

Endianness specifies the order which the data is stored in

the memory by processor operations in a multi byte system.

Based on Endiannes processors can be of two types:

1.Little Endian Processors

2. Big Endian Processors

Little endian means lower order data byte is stored in memory at the lowest address and the higher order data byte at the highest address. For e.g, 4 byte long integer Byte3, Byte2, Byte1, Byte0 will be store in the memory as

follows:

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PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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Base address+0 Byte 0

Base address+1 Byte 1

Base address+2 Byte 2

Base address+3 Byte 3

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CONTD

  • Big endian means the higher order data byte is stored in memory at the lowest and the lower order data byte at the highest address. For e.g. a 4 byte integer Byte3, Byte2, Byte1, Byte0 will be stored in the memory as follows:
  • Base address+0 Byte 3
  • Base address+1 Byte 2
  • Base address+2 Byte 1
  • Base address+3 Byte 0

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MICROCONTROLLERS.��

  • A microcontroller is a highly integrated chip that contains a CPU, scratch pad RAM, special and general purpose register arrays , on chip ROM/FLASH memory for program storage , timer and interrupt control units and dedicated I/O ports.
  • Some embedded system application require only 8 bit controllers whereas some requiring superior performance and computational needs demand 16/32 bit controllers
  • The instruction set of a microcontroller can be RISC or CISC.
  • �Microcontrollers are designed for either general purpose application requirement or domain specific application requirement.

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DIGITAL SIGNAL PROCESSORS�

DSP are powerful special purpose 8/16/32 bit microprocessor designed to meet the computational demands and power constraints of today’s embedded audio, video and communication applications

DSPs implement algorithms in hardware which speeds up the execution whereas general purpose processor implement the algorithm in software and the speed of execution depends primarily on the clock for the processors.

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KEY UNITS OF DSP

  • Program memory:
  • Data memory:
  • Computational engine:
  • I/O unit:

Examples:

Audio video signal processing, telecommunication and multimedia applications.

SOP(Sum of Products) calculation, convolution, FFT(Fast Fourier Transform), DFT(Discrete Fourier Transform), etc are some of the operation performed by DSP.

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APPLICATION SPECIFIC INTEGRATED CIRCUITS.�(ASIC)��

  • ASICs is a microchip design to perform a specific and unique applications.

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  • Because of using single chip for integrates several functions there by reduces the system development cost.

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  • Most of the ASICs are proprietary (which having some trade name) products, it is referred as Application Specific Standard Products(ASSP).

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  • As a single chip ASIC consumes a very small area in the total system. Thereby helps in the design of smaller system with high capabilities or functionalities.

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PLD’S

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A PLD is an electronic component. It used to build digital circuits which are reconfigurable.

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PLDs are of two major types

1)CPLD(Complex Programmable Logic Device):

  • CPLDs offer much smaller amount of logic up to 1000 gates.

2)FPGAs(Field Programmable Gate Arrays):

  • It offers highest amount of performance as well as highest logic density, the most features.

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COMMERCIAL -OFF -THE-SHELF COMPONENTS(COTS)�

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The COTS components are developed around a general purpose or domain specific processor or an ASICs or a PLDs.

Advantages of COTS:

1)Ready to use

2)Easy to integrate

3)Reduces development time

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Disadvantages of COTS:

1)No operational or manufacturing standard (all proprietary)

2)Vendor or manufacturer may discontinue production of a particular COTS product

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  • �

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MEMORY TYPES

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    • Secondary Memory
    • Primary Memory

RAM

SRAM

        • DRAM
      • ROM
        • PROM
        • EPROM
      • Hybrid
        • EEPROM
        • NVRAM
        • Flash Memory
      • Cache Memory
      • Virtual Memory
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SECONDARY MEMORY

The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also an order of magnitude less expensive than primary storage.

  • The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information. Hard disk are usually used as secondary storage.
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PRIMARY MEMORY

  • Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required.
  • Main memory is directly or indirectly connected to the CPU via a memory bus. It is actually two buses (not on the diagram): an address bus and a data bus. The CPU firstly sends a number through an address bus, a number called memory address, that indicates the desired location of data. Then it reads or writes the data itself using the data bus.
  • It is divided into RAM and ROM.

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RAM(DATA MEMORY OR WORKING MEMORY)

  • RAM is a direct access memory, meaning we can access the desired memory location directly without the need for traversing through the entire memory locations to reach the desired memory position (i.e. Random Access of memory location)

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�STATIC RAM (SRAM): �

  • Static RAM stores data in the form of Voltage.
  • They are made up of flip-flops
  • Static RAM is the fastest form of RAM available
  • SRAM is fast in operation due to its resistive networking and switching capabilities

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�DYNAMIC RAM (DRAM) �

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  • Dynamic RAM stores data in the form of charge. They are made up of MOS transistor gates

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  • The advantages of DRAM are its high density and low cost compared to SRAM

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  • The disadvantage is that since the information is stored as charge it gets leaked off with time and to prevent this they need to be refreshed periodically

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  • Special circuits called DRAM controllers are used for the refreshing operation. The refresh operation is done periodically in milliseconds interval

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�NON VOLATILE RAM (NVRAM): �

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  • Random access memory with battery backup
  • It contains Static RAM based memory and a minute battery for providing supply to the memory in the absence of external power supply
  • The memory and battery are packed together in a single package
  • NVRAM is used for the non volatile storage of results of operations or for setting up of flags etc
  • The life span of NVRAM is expected to be around 10 years

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PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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MEMORY SELECTION FOR EMBEDDED SYSTEMS:

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  • Selection of suitable memory is very much essential step in high performance applications, because the challenges and limitations of the system performance are often decided upon the type of memory architecture.

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  • Systems memory requirement depend primarily on the nature of the application that is planned to run on the system.

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  • Memory performance and capacity requirement for low cost systems are small, whereas memory throughput can be the most critical requirement in a complex, high performance system.

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MEMORY SELECTION FOR EMBEDDED SYSTEMS:

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  • Selection of suitable memory is very much essential step in high performance applications, because the challenges and limitations of the system performance are often decided upon the type of memory architecture.

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  • Systems memory requirement depend primarily on the nature of the application that is planned to run on the system.

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  • Memory performance and capacity requirement for low cost systems are small, whereas memory throughput can be the most critical requirement in a complex, high performance system.

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Following are the factors that are to be considered while selecting the memory devices,

  • Speed
  • Data storage size and capacity
  • Bus width
  • Power consumption
  • Cost

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TYPES OF ROM

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  • Memories in the ROM family are distinguished by the methods used to write new data to them (usually called programming), and the number of times they can be rewritten.
  • This classification reflects the evolution of ROM devices from hardwired to programmable to erasable-and-programmable. A common feature is their ability to retain data and programs forever, even during a power failure.
  • The contents of the ROM had to be specified before chip production, so the actual data could be used to arrange the transistors inside the chip.

 

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PROM

  • One step up from the masked ROM is the PROM (programmable ROM), which is purchased in an unprogrammed state. If you were to look at the contents of an unprogrammed PROM, the data is made up entirely of 1's.
  • The process of writing your data to the PROM involves a special piece of equipment called a device programmer. The device programmer writes data to the device one word at a time by applying an electrical charge to the input pins of the chip.
  • Once a PROM has been programmed in this way, its contents can never be changed. If the code or data stored in the PROM must be changed, the current device must be discarded. As a result,
  • PROMs are also known as one-time programmable (OTP) devices.

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EEPROM

    • An EPROM (erasable-and-programmable ROM) is programmed in exactly the same manner as a PROM. However, EPROMs can be erased and reprogrammed repeatedly.
    • To erase an EPROM, you simply expose the device to a strong source of ultraviolet light. (A window in the top of the device allows the light to reach the silicon.)
    • By doing this, you essentially reset the entire chip to its initial-un programmed-state. Though more expensive than PROMs, their ability to be reprogrammed makes EPROMs an essential part of the software development and testing process.

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PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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DIFFERENCES BETWEEN SRAM & DRAM

PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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SRAM

DRAM

Made up to 6 CMOS Transistors

Made up of MOSFET and capacitor

Doesn't require refreshing

Require refreshing

Low capacitance (less dense)

High capacitance(Highly dense)

More expensive

Less expensive

Fast in operation(10 ns)

Slow in operation (60 ns)

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SENSORS &ACTUATORS�

Sensor

A Sensor is used for taking Input

It is a transducer that converts energy from one form to another for any measurement or control

purpose

Ex. A Temperature sensor

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PRIYANKA YADLAPALLI,Dept of ECE,GRIET

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ACTUATORS

Actuator is used for output.

It is a transducer that may be either mechanical or electrical which converts signals to corresponding physical actions.

Ex. LED (Light Emitting Diode)

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  • This ppt is purely for academic purpose

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