Embedded Systems (18EC62) – Embedded System Components (Module 3)

Embedded System
Components
EMBEDDED SYSTEMS (18EC62)
MODULE – 3
1
Shrishail Bhat, Dept. of ECE, AITM Bhatkal

Introduction
2

What is an Embedded System?
• An embedded system is an electronic/electro-mechanical
system designed to perform a specific function and is a
combination of both hardware and firmware (software).
• Every embedded system is unique and the hardware as
well as the firmware is highly specialised to the application
domain.
3

Embedded Systems vs. General
Computing Systems
• The computing revolution began with the general purpose
computing requirements. Later it was realised that the
general computing requirements are not sufficient for the
embedded computing requirements.
• The embedded computing requirements demand
‘something special’ in terms of response to stimuli,
meeting the computational deadlines, power efficiency,
limited memory capability, etc.
4

General Purpose Computing System Embedded System
A system which is a combination of a generic hardware
and a General Purpose Operating System for executing a
variety of applications
A system which is a combination of special purpose
hardware and embedded OS for executing a specific set of
applications
Contains a General Purpose Operating System (GPOS) May or may not contain an operating system for
functioning
Applications are alterable (programmable) by the user (It
is possible for the end user to re-install the operating
system, and also add or remove user applications)
The firmware of the embedded system is pre-programmed
and it is non-alterable by the end-user (There may be
exceptions for system supporting OS kernel image flashing
through special hardware settings)
Performance is the key deciding factor in the selection of
the system. Always, ‘Faster is Better’
Application-specific requirements (like performance,
power requirements, memory usage, etc.) are the key
deciding factors
Less/not at all tailored towards reduced operating power
requirements, options for different levels of power
management
Highly tailored to take advantage of the power saving
modes supported by the hardware and the operating
system
Response requirements are not time-critical For certain category of embedded systems like mission
critical systems, the response time requirement is highly
critical
Need not be deterministic in execution behaviour Execution behaviour is deterministic for certain types of
embedded systems like ‘Hard Real Time’ systems
5

History of Embedded Systems
• Embedded systems were in existence even before the IT revolution.
• Built around the old vacuum tube and transistor technologies.
• Advances in semiconductor and nanotechnology and IT revolution gave way to the
development of miniature embedded systems.
• The first recognised modern embedded system is the Apollo Guidance Computer (AGC)
developed by the MIT Instrumentation Laboratory for the lunar expedition.
• It had 36K words of fixed memory and 2K words of erasable memory.
• The clock frequency of was 1.024 MHz and it was derived from a 2.048 MHz crystal
clock.
• The first mass-produced embedded system was the Autonetics D-17 guidance
computer for the Minuteman-I missile in 1961.
• It was built using discrete transistor logic and a hard-disk for main memory.
• The first integrated circuit was produced in September 1958 and computers using them
began to appear in 1963.
6

Classification of Embedded Systems
• Some of the criteria used in the classification of embedded
systems are:
1. Based on generation
2. Complexity and performance requirements
3. Based on deterministic behaviour
4. Based on triggering
7

Classification Based on Generation
• First Generation
• Second Generation
• Third Generation
• Fourth Generation
• Next Generation
8

(continued)
• First Generation
• Early embedded systems were built around 8-bit microprocessors
like 8085 and Z80 and 4-bit microcontrollers.
• Simple in hardware circuits with firmware developed in assembly
code.
• E.g.: Digital telephone keypads, stepper motor control units, etc.
9

(continued)
• Second Generation
• Embedded systems built around 16-bit microprocessors and 8-bit
or 16-bit microcontrollers.
• Instruction set were much more complex and powerful than the
first generation.
• Some of the second generation embedded systems contained
embedded operating systems for their operation.
• E.g.: Data acquisition systems, SCADA systems, etc.
10

(continued)
• Third Generation
• Embedded systems built around 32-bit microprocessors and 16-bit
microcontrollers.
• Application and domain specific processors/controllers like Digital
Signal Processors (DSP) and Application Specific Integrated Circuits
(ASICs) came into picture.
• The instruction set of processors became more complex and powerful
and the concept of instruction pipelining also evolved.
• Dedicated embedded real time and general purpose operating systems
entered into the embedded market.
• Embedded systems spread its ground to areas like robotics, media,
industrial process control, networking, etc.
11

(continued)
• Fourth Generation
• The advent of System on Chips (SoC), reconfigurable processors
and multicore processors are bringing high performance, tight
integration and miniaturisation into the embedded device
market.
• The SoC technique implements a total system on a chip by
implementing different functionalities with a processor core on
an integrated circuit.
• They make use of high performance real time embedded
operating systems for their functioning.
• E.g.: Smart phone devices, Mobile Internet Devices (MIDs), etc.
12

(continued)
• Next Generation
• The processor and embedded market is highly dynamic and
demanding.
• The next generation embedded systems are expected to meet
growing demands in the market.
13

Classification Based on Complexity and
Performance
• Small-Scale Embedded Systems
• Medium-Scale Embedded Systems
• Large-Scale Embedded Systems/Complex Systems
14

Performance (continued)
• Small-Scale Embedded Systems
• Simple in application needs and the performance requirements
are not time critical.
• E.g.: An electronic toy
• Usually built around low performance and low cost 8-bit or 16-bit
microprocessors/microcontrollers.
• May or may not contain an operating system for its functioning.
15

• Medium-Scale Embedded Systems
• Slightly complex in hardware and firmware (software)
requirements.
• Usually built around medium performance, low cost 16-bit or 32-
bit microprocessors/microcontrollers or digital signal processors.
• Usually contain an embedded operating system (either general
purpose or real time operating system) for functioning.
16

• Large-Scale Embedded Systems/Complex Systems
• Highly complex in hardware and firmware (software) requirements.
• They are employed in mission critical applications demanding high
performance.
• Usually built around high performance 32-bit or 64-bit RISC
processors/controllers or Reconfigurable System on Chip (RSoC) or multi-
core processors and programmable logic devices.
• May contain multiple processors/controllers and co-units/hardware
accelerators for offloading the processing requirements from the main
processor of the system.
• Decoding/encoding of media, cryptographic function implementation, etc.
are examples of processing requirements which can be implemented using a
co-processor/hardware accelerator.
• Usually contain a high performance real time operating system (RTOS) for
task scheduling, prioritization and management.
17

Classification Based on Deterministic
Behaviour
• Applicable for ‘Real Time’ systems.
• The application/task execution behaviour can be either
deterministic or non-deterministic.
• Based on the execution behaviour, real time embedded systems are
classified into Hard Real Time and Soft Real Time systems.
18

Classification Based on Triggering
• Embedded systems which are ‘Reactive’ in nature (like process
control systems in industrial control applications) can be classified
based on the trigger.
• Reactive systems can be either event-triggered or time-triggered.
19

Major Application Areas of Embedded
Systems
1. Consumer electronics: Camcorders, cameras, etc.
2. Household appliances: Television, DVD players, washing machine,
refrigerators, microwave oven, etc.
3. Home automation and security systems: Air conditioners,
sprinklers, intruder detection alarms, closed circuit television
(CCTV) cameras, fire alarms, etc.
4. Automotive industry: Anti-lock braking systems (ABS), engine
control, ignition systems, automatic navigation systems, etc.
5. Telecom: Cellular telephones, telephone switches, handset
multimedia applications, etc.
20

Systems (continued)
6. Computer peripherals: Printers, scanners, fax machines, etc.
7. Computer networking systems: Network routers, switches, hubs,
firewalls, etc.
8. Healthcare: Different kinds of scanners, EEG, ECG machines, etc.
9. Measurements & Instrumentation: Digital multimeters, digital
CROs, logic analyzers, PLC systems, etc.
10. Banking & Retail: Automated teller machines (ATM) and currency
counters, point of sales (POS), etc.
11. Card readers: Barcode, smart card readers, hand held devices, etc.
21

Systems (continued)
12. Wearable Devices: Health and fitness trackers, Smartphone
screen extension for notifications, etc.
13. Cloud Computing and Internet of Things (IoT)
22

Purpose of Embedded Systems
• Each embedded system is designed to serve the purpose of any one
or a combination of the following tasks:
1. Data Collection/Storage/Representation
2. Data Communication
3. Data (Signal) Processing
4. Monitoring
5. Control
6. Application Specific User Interface
23

(continued)
• Data Collection/Storage/Representation
• Embedded systems designed for the purpose of
data collection performs acquisition of data from
the external world.
• Data collection is usually done for storage,
analysis, manipulation and transmission.
• The term "data" refers all kinds of information,
viz. text, voice, image, video, electrical signals and
any other measurable quantities.
• Data can be either analog (continuous) or digital
(discrete).
• The collected data may be stored or transmitted
or it may be processed or it may be deleted
instantly after giving a meaningful representation.
• A digital camera is a typical
example of an embedded system
with data
collection/storage/representation
of data.
• Images are captured and the
captured image may be stored
within the memory of the camera.
• The captured image can also be
presented to the user through a
graphic LCD unit.
24

(continued)
• Data Communication
• Embedded data communication systems are
deployed in applications ranging from complex
satellite communication systems to simple
home networking systems.
• The transmission is achieved either by a wire-
line medium or by a wireless medium.
• The data collecting embedded terminal itself
can incorporate data communication units like
wireless modules (Bluetooth, ZigBee, Wi-Fi,
EDGE, GPRS, etc.) or wire-line modules (RS-
232C, USB, TCP/IP, PS2, etc.).
Fig: A wireless network router for
data communication
• Network hubs, routers, switches,
etc. are typical examples of
dedicated data transmission
embedded systems.
• They act as mediators in data
communication and provide
various features like data security,
monitoring etc.
25

(continued)
• Data (Signal) Processing
• The data (voice, image, video, electrical signals
and other measurable quantities) collected by
embedded systems may be used for various
kinds of data processing.
• Embedded systems with signal processing
functionalities are employed in applications
demanding signal processing like speech
coding, synthesis, audio video codec,
transmission applications, etc.
• A digital hearing aid is a typical
example of an embedded system
employing data processing.
• Digital hearing aid improves the
hearing capacity of hearing
impaired persons.
26

(continued)
• Monitoring
• Almost embedded products coming under the medical
domain are used for monitoring.
• A very good example is the electro cardiogram (ECG)
machine for monitoring the heartbeat of a patient.
• The machine is intended to do the monitoring of the heartbeat.
• It cannot impose control over the heartbeat.
• The sensors used in ECG are the different electrodes connected
to the patient's body.
• Some other examples of embedded systems with
monitoring function are measuring instruments like
digital CRO, digital multimeters, logic analyzers, etc.
used in Control & Instrumentation applications.
Fig: A patient monitoring system for
monitoring heartbeat
27

(continued)
• Control
• Embedded systems with control functionalities
impose control over some variables according to
the changes in input variables.
• A system with control functionality contains both
sensors and actuators.
• Sensors are connected to the input port for
capturing the changes in environmental variable
or measuring variable.
• The actuators connected to the output port are
controlled according to the changes in input
variable to put an impact on the controlling
variable to bring the controlled variable to the
specified range.
• An Air Conditioner System used to
control the room temperature to
a specified limit is a typical
example for embedded system for
control purpose.
• An air conditioner contains a
room temperature-sensing
element (sensor) which may be a
thermistor and a handheld unit
for setting up (feeding) the
desired temperature.
28

(continued)
• Application Specific User Interface
• These are embedded systems with
application-specific user interfaces like
buttons, switches, keypad, lights, bells, display
units, etc.
• Mobile phone is an example for this.
• In mobile phone the user interface is provided
through the keypad, graphic LCD module,
system speaker, vibration alert, etc.
• A mobile phone is an example for
embedded system with an
application-specific user
interfaces.
29

The Typical Embedded
System
ELEMENTS OF AN EMBEDDED SYSTEM
30

The Typical Embedded System
Fig: Elements of an Embedded System
31

(continued)
32
• It contains a single chip controller, which acts as the master brain of
the system.
• The controller can be
✓ A microprocessor or
✓ A microcontroller or
✓ A Field Programmable Gate Array (FPGA) device or
✓ A Digital Signal Processor (DSP) or
✓ An Application Specific Integrated Circuit (ASIC)/Application Specific
Standard Product (ASSP)

(continued)
33
• An embedded system can be viewed as a reactive system.
• The control is achieved by processing the information coming from
the sensors and user interfaces, and controlling some actuators
that regulate the physical variable.
• Key boards, push button switches, etc. are examples for common
user interface input devices.
• LEDs, liquid crystal displays, piezoelectric buzzers, etc. are examples
for common user interface output devices for a typical embedded
system.

(continued)
34
• The memory of the system is responsible for holding the control algorithm and other
important configuration details.
• For most of embedded systems, the memory for storing the algorithm or configuration data is
of fixed type, which is a kind of Read Only Memory (ROM).
• It is not available for the end user for modifications
• The memory is protected from unwanted user interaction by implementing some kind of
memory protection mechanism.
• The most common types of memories used in embedded systems for control algorithm
storage are OTP, PROM, UVEPROM, EEPROM and FLASH.
• Sometimes the system requires temporary memory for performing arithmetic operations or
control algorithm execution and this type of memory is known as "working memory".
• Random Access Memory (RAM) is used in most of the systems as the working memory.
• Various types of RAM like SRAM, DRAM and NVRAM are used for this purpose.

(continued)
35
• Apart from these, communication interface is essential for
communicating with various subsystems of the embedded system
and with the external world.
• The communication interfaces may be used to achieve onboard
(I2C, SPI, UART, parallel bus interface, etc.) or external
communication (wireless interfaces like Infrared, Bluetooth, Wi-Fi,
etc.)

RISC vs. CISC Processors/Controllers
• RISC stands for Reduced Instruction Set Computing.
• All RISC processors/controllers possess lesser number of instructions,
typically in the range of 30 to 40.
• E.g.: Atmel AVR microcontroller – its instruction set contains only 32
instructions.
• CISC stands for Complex Instruction Set Computing.
• The instruction set is complex and instructions are high in number.
• E.g.: 8051 microcontroller – its instruction set contains 255
instructions.
36

RISC CISC
Lesser number of instructions Greater number of instructions
Instruction pipelining and increased execution speed Generally no instruction pipelining feature
Orthogonal instruction set (Allows each instruction to operate on
any register and use any addressing mode)
Non-orthogonal instruction set (All instructions are not allowed to
operate on any register and use any addressing mode. It is
instruction-specific)
Operations are performed on registers only, the only memory
operations are load and store
Operations are performed on registers or memory depending on the
instruction
A large number of registers are available Limited number of general purpose registers
Programmer needs to write more code to execute a task since the
instructions are simpler ones
Instructions are like macros in C language. A programmer can
achieve the desired functionality with a single instruction which in
turn provides the effect of using more simpler single instructions in
RISC
Single, fixed length instructions Variable length instructions
Less silicon usage and pin count More silicon usage since more additional decoder logic is required
to implement the complex instruction decoding
With Harvard Architecture Can be Harvard or Von-Neumann Architecture
37

Harvard vs. Von-Neumann
Processor/ControIIer Architecture
• Von-Neumann Architecture
• Microprocessors/controllers based on the Von-Neumann architecture
share a single common bus for fetching both instructions and data.
• Program instructions and data are stored in a common main memory.
• They first fetch an instruction and then fetch the data to support the
instruction from code memory.
• The two separate fetches slows down the controller's operation.
• Von-Neumann architecture is also referred as Princeton architecture,
since it was developed by the Princeton University.
38

Processor/ControIIer Architecture (continued)
• Harvard Architecture
• Microprocessors/controllers based on the Harvard architecture will
have separate data bus and instruction bus.
• This allows the data transfer and program fetching to occur simultaneously on
both buses.
• The data memory can be read and written while the program memory
is being accessed.
• These separated data memory and code memory buses allow one
instruction to execute while the next instruction is fetched ("pre-
fetching").
• The pre-fetch theoretically allows much faster execution than Von-Neumann
architecture.
39

Processor/ControIIer Architecture (continued)
Harvard Architecture Von-Neumann Architecture
Separate buses for instruction and data fetching Single shared bus for instruction and data fetching
Easier to pipeline, so high performance can be
achieved
Low performance compared to Harvard
architecture
Comparatively high cost Cheaper
No memory alignment problems Allows self modifying codes
Since data memory and program memory are
stored physically in different locations, no chances
for accidental corruption of program memory
Since data memory and program memory are
stored physically in the same chip, chances for
accidental corruption of program memory
40

Big-Endian vs. Little-Endian
Processors/Controllers
• Endianness specifies the order in which the data is stored in the
memory by processor operations in a multi byte system.
• Suppose the word length is two byte then data can be stored in
memory in two different ways:
1. Higher order of data byte at the higher memory and lower order of
data byte at location just below the higher memory – Little-Endian
◦ E.g.: Intel x86 Processors
2. Lower order of data byte at the higher memory and higher order of
data byte at location just below the higher memory – Big-Endian
◦ E.g.: Motorola 68000 Series Processors
41

Processors/Controllers (continued)
• Little-endian means the lower-order byte of the data is stored in
memory at the lowest address, and the higher-order byte at the
highest address. (The little end comes first.)
• For example, a 4 byte long integer Byte3 Byte2 Byte1 Byte0 will be
stored in the memory as shown below:
42

• Big-endian means the higher-order byte of the data is stored in
memory at the lowest address, and the lower-order byte at the
highest address. (The big end comes first.)
• For example, a 4 byte long integer Byte3 Byte2 Byte1 Byte0 will be
stored in the memory as shown below:
43

• Consider data 43675829H
44
29
58
67
43
43
67
58
29
Little-Endian Big-Endian

Memory
45

Memory
• Memory is an important part of a processor/controller based
embedded systems.
• Some of the processors/controllers contain built in memory and
this memory is referred as on-chip memory.
• Others do not contain any memory inside the chip and requires
external memory to be connected with the controller/processor to
store the control algorithm. It is called off-chip memory.
• Also some working memory is required for holding data temporarily
during certain operations.
46

Program Storage Memory (ROM)
• The program memory or code storage memory of an embedded system
stores the program instructions.
• The code memory retains its contents even after the power is turned off.
It is generally known as non-volatile storage memory.
• It can be classified into different types as shown:
47

Masked ROM (MROM)
• Masked ROM is a one-time programmable device.
• Masked ROM makes use of the hardwired technology for storing data.
• The device is factory programmed by masking and metallisation process
at the time of production itself, according to the data provided by the
end user.
• Advantage – low cost for high volume production.
• Limitation – inability to modify the device firmware against firmware
upgrades.
• Since the MROM is permanent in bit storage, it is not possible to alter the bit
information.
48

Masked ROM (MROM) (continued)
• Different mechanisms are used for the masking process of the
ROM, like
1. Creation of an enhancement or depletion mode transistor
through channel implant.
2. By creating the memory cell either using a standard transistor or
a high threshold transistor.
• In the high threshold mode, the supply voltage required to turn ON
the transistor is above the normal ROM IC operating voltage.
• This ensures that the transistor is always off and the memory cell
stores always logic 0.
49

Programmable Read Only Memory
(PROM) / (OTP)
• One Time Programmable Memory (OTP) or PROM is not pre-programmed by
the manufacturer.
• The end user is responsible for programming these devices.
• This memory has nichrome or polysilicon wires arranged in a matrix. These
wires can be functionally viewed as fuses.
• It is programmed by a PROM programmer which selectively burns the fuses
according to the bit pattern to be stored.
• Fuses which are not blown/burned represents a logic “1" whereas fuses which are
blown/burned represents a logic 0 .
• The default state is logic "1".
• OTP is widely used for commercial production of embedded systems whose
prototyped versions are proven and the code is finalised.
• It is a low cost solution for commercial production.
• OTPs cannot be reprogrammed.
50

Erasable Programmable Read Only
Memory (EPROM)
• Erasable Programmable Read Only Memory (EPROM) gives the flexibility
to re-program the same chip.
• EPROM stores the bit information by charging the floating gate of an FET.
• Bit information is stored by using an EPROM programmer, which applies
high voltage to charge the floating gate.
• EPROM contains a quartz crystal window for erasing the stored
information.
• If the window is exposed to ultraviolet rays for a fixed duration, the entire
memory will be erased.
• Even though the EPROM chip is flexible in terms of re-programmability, it
needs to be taken out of the circuit board and put in a UV eraser device
for 20 to 30 minutes.
• It is a tedious and time-consuming process.
51

Electrically Erasable Programmable Read
only Memory (EEPROM)
• The information contained in the EEPROM memory can be altered
by using electrical signals at the register/byte level.
• They can be erased and reprogrammed in-circuit.
• These chips include a chip erase mode and in this mode they can be
erased in a few milliseconds.
• It provides greater flexibility for system design.
• The only limitation is their capacity is limited (a few kilobytes) when
compared with the standard ROM.
52

FLASH
• FLASH memory is a variation of EEPROM technology – It combines the re-
programmability of EEPROM and the high capacity of standard ROMs.
• FLASH is the latest ROM technology.
• Most popular ROM technology used in today's embedded designs.
• FLASH memory is organised as sectors (blocks) or pages.
• FLASH memory stores information in an array of floating gate MOSFET transistors.
• The erasing of memory can be done at sector level or page level without affecting the
other sectors or pages.
• Each sector/page should be erased before re-programming.
• The typical erasable capacity of FLASH is of the order of a few thousand cycles.
• E.g.: SST39LF010 from Microchip is an example of 1Mbit (organised as 128Kx8) FLASH
memory with typical endurance of 100,000 cycles.
53

Non-Volatile RAM (NVRAM)
• Non-volatile RAM is a 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.
• The life span of NVRAM is expected to be around 10 years.
• E.g.: DS1644 from Maxim/Dallas is an example of 32KB NVRAM.
54

Read-Write Memory/Random Access
Memory (RAM)
• RAM is the data memory or working memory of the controller/processor.
• Controller/processor can read from it and write to it.
• RAM is volatile – when the power is turned off, all the contents are
destroyed.
• RAM is a direct access memory – 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).
• This is in contrast to the Sequential Access Memory (SAM), where the desired
memory location is accessed by either traversing through the entire memory
or through a 'seek' method. Magnetic tapes, CD ROMs, etc. are examples of
sequential access memories.
55

Read-Write Memory/Random Access
Memory (RAM) (continued)
• RAM generally falls into three categories: Static RAM (SRAM),
Dynamic RAM (DRAM) and Non-Volatile RAM (NVRAM).
56

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.
• Fast due to its resistive networking and switching capabilities.
• In typical implementation, an SRAM cell (bit) is realised using six
transistors (or 6 MOSFETs).
• Four of the transistors are used for building the latch (flip-flop) part of
the memory cell and two for controlling the access.
57

Static RAM (SRAM) (continued)
• In its simplest representation an SRAM cell can be visualised as
shown in the figure below:
Fig: SRAM cell implementation
58

• This implementation in its simpler form can be visualised as two
cross-coupled inverters with read/write control through transistors.
• The four transistors in the middle form the cross-coupled inverters.
• This can be visualised as shown in the figure below:
Fig: Visualisation of SRAM cell
59

• The access to the memory cell is controlled by Word Line, which
controls the access transistors (MOSFETs) Q5 and Q6.
• The access transistors control the connection to bit lines B & B.
• In order to write a value to the memory cell, apply the desired value
to the bit control lines (For writing 1, make B = 1 and B = 0; For
writing 0, make B = 0 and B = 1) and assert the Word Line (Make
Word line high).
• This operation latches the bit written in the flip-flop.
• For reading the content of the memory cell, assert both B and B bit
lines to 1 and set the Word line to 1.
• The major limitations of SRAM are low capacity and high cost.
60

Dynamic RAM (DRAM)
• Dynamic RAM stores data in the form of charge.
• They are made up of MOS transistor gates.
• Advantages – high density and low cost compared to SRAM.
• Disadvantage – since the information is stored as charge it gets
leaked off with time and to prevent this they need to be refreshed
periodically.
• Special circuits called DRAM controllers are used for the refreshing
operation.
• The refresh operation is done periodically in milliseconds interval.
61

Dynamic RAM (DRAM) (continued)
• Figure below illustrates the typical implementation of a DRAM cell.
• The MOSFET acts as the gate for the incoming and outgoing data
whereas the capacitor acts as the bit storage unit.
Fig: DRAM cell implementation
62

SRAM vs DRAM
• Table given below summarises the relative merits and demerits of
SRAM and DRAM technology.
SRAM Cell DRAM Cell
Made up of 6 CMOS transistors (MOSFET) Made up of a MOSFET and a capacitor
Doesn't require refreshing Requires refreshing
Low capacity (Less dense) High capacity (Highly dense)
More expensive Less expensive
Fast in operation. Typical access time is 10ns Slow in operation due to refresh requirements.
Typical access time is 60ns. Write operation is faster
than read operation.
63

Non-Volatile RAM (NVRAM)
• Non-volatile RAM is a 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.
• The life span of NVRAM is expected to be around 10 years.
• E.g.: DS1644 from Maxim/Dallas is an example of 32KB NVRAM.
64

Sensors and Actuators
65

Sensors and Actuators
• An embedded system is in constant interaction with the real world
and the controlling/monitoring functions executed by the embedded
system is achieved in accordance with the changes happening to the
real world.
• The changes in system environment or variables are detected by the
sensors connected to the input port of the embedded system.
• If the embedded system is designed for any controlling purpose, the
system will produce some changes in the controlling variable to bring
the controlled variable to the desired value.
• It is achieved through an actuator connected to the output port of the
embedded system.
66

Sensors and Actuators (continued)
• A sensor is a transducer device that converts energy from one form
to another for any measurement or control purpose.
• E.g.: Temperature sensor, magnetic hall effect sensor, humidity sensor,
etc.
• An actuator is a form of transducer device (mechanical or electrical)
which converts signals to corresponding physical action (motion).
• Actuator acts as an output device.
• E.g.: Stepper motor
67

Optocoupler
• Optocoupler is a solid state device to isolate two parts of a circuit.
• Optocoupler combines an LED and a photo-transistor in a single
housing.
• Figure illustrates the functioning of an optocoupler device.
Fig: An optocoupler device
68

Optocoupler (continued)
• In electronic circuits, an optocoupler is used for suppressing
interference in data communication, circuit isolation, high voltage
separation, simultaneous separation and signal intensification, etc.
• Optocouplers can be used in either input circuits or in output
circuits.
• Optocoupler is available as ICs from different semiconductor
manufacturers.
• The MCT2M IC from Fairchild semiconductor is an example for
optocoupler IC.
69

Optocoupler (continued)
• Figure illustrates the usage of optocoupler in input circuit and
output circuit of an embedded system with a microcontroller as the
system core.
Fig: Optocoupler in Input and Output circuit
70

Communication
Interface
71

Communication Interface
• Communication interface is essential for communicating with various
subsystems of the embedded system and with the external world.
• For an embedded product, the communication interface can be viewed
in two different perspectives:
• Onboard Communication Interface (Device/board level communication
interface)
• E.g.: Serial interfaces like I2C, SPI, UART, 1-Wire, etc and parallel bus interface.
• External Communication Interface (Product level communication interface)
• E.g.: Wireless interfaces like Infrared (IR), Bluetooth (BT), Wireless LAN (Wi-Fi), Radio
Frequency waves (RF), GPRS, etc. and wired interfaces like RS-232C/RS-422/RS-485, USB,
Ethernet IEEE 1394 port, Parallel port, CF-II interface, SDIO, PCMCIA/PCIex, etc.
72

Onboard Communication Interfaces
• An embedded system is a combination of different types of
components (chips/devices) arranged on a printed circuit board
(PCB).
• Onboard Communication Interface refers to the different
communication channels/buses for interconnecting the various
integrated circuits and other peripherals within the embedded
system.
• E.g.: Serial interfaces like I2C, SPI, UART, 1-Wire, etc and parallel bus
interface
73

Inter Integrated Circuit (I2C) Bus
• The Inter Integrated Circuit Bus (I2C or I2C Pronounced 'I square C') is a
synchronous bi-directional half duplex two wire serial interface bus.
• (Half duplex - one-directional communication at a given point of time)
• The concept of I2C bus was developed by Philips Semiconductors in the
early 1980s.
• The original intention of I2C was to provide an easy way of connection
between a microprocessor/microcontroller system and the peripheral
chips in television sets.
• The I2C bus comprise of two bus lines:
• Serial Clock (SCL line) – responsible for generating synchronisation clock pulses
• Serial Data (SDA line) – responsible for transmitting the serial data across devices
74

(continued)
• I2C bus is a shared bus system to which many number of I2C devices can
be connected.
• Devices connected to the I2C bus can act as either 'Master' or 'Slave’.
• The 'Master' device is responsible for controlling the communication by
initiating/terminating data transfer, sending data and generating necessary
synchronisation clock pulses.
• 'Slave' devices wait for the commands from the master and respond upon
receiving the commands.
• 'Master' and 'Slave' devices can act as either transmitter or receiver.
• Regardless whether a master is acting as transmitter or receiver, the
synchronisation clock signal is generated by the 'Master' device only.
• I2C supports multi masters on the same bus.
75

(continued)
• The following bus interface diagram illustrates the connection of
master and slave devices on the I2C bus.
Fig: I2C Bus Interfacing
76

(continued)
• The I2C bus interface is built around an input buffer and an open drain or
collector transistor.
• When the bus is in the idle state, the open drain/collector transistor will be in
the floating state and the output lines (SDA and SCL) switch to the 'High
Impedance' state.
• For proper operation of the bus, both the bus lines should be pulled to the
supply voltage (+5 V for TTL family and +3.3V for CMOS family devices) using
pull-up resistors.
• The typical value of resistors used in pull-up is 2.2K.
• With pull-up resistors, the output lines of the bus in the idle state will be 'HIGH'
• The address of a I2C device is assigned by hardwiring the address lines of the
device to the desired logic level.
• Done at the time of designing the embedded hardware.
77

(continued)
• The sequence of operations for communicating with an I2C slave
device is listed below:
1. The master device pulls the clock line (SCL) of the bus to 'HIGH'
2. The master device pulls the data line (SDA) 'LOW', when the SCL line is
at logic 'HIGH' (This is the 'Start' condition for data transfer)
3. The master device sends the address (7 bit or 10 bit wide) of the
'slave' device to which it wants to communicate, over the SDA line.
◦ Clock pulses are generated at the SCL line for synchronising the bit reception by
the slave device.
◦ The MSB of the data is always transmitted first.
◦ The data in the bus is valid during the 'HIGH' period of the clock signal
78

(continued)
4. The master device sends the Read or Write bit (Bit value = 1 Read operation; Bit
value = 0 Write operation) according to the requirement
5. The master device waits for the acknowledgement bit from the slave device whose
address is sent on the bus along with the Read/ Write operation command.
◦ Slave devices connected to the bus compares the address received with the address assigned
to them
6. The slave device with the address requested by the master device responds by
sending an acknowledge bit (Bit value 1) over the SDA line
7. Upon receiving the acknowledge bit, the Master device sends the 8 bit data to the
slave device over SDA line, if the requested operation is 'Write to device’.
◦ If the requested operation is 'Read from device', the slave device sends data to the master
over the SDA line
8. The master device waits for the acknowledgement bit from the device upon byte
transfer complete for a write operation and sends an acknowledge bit to the Slave
device for a read operation
9. The master device terminates the transfer by pulling the SDA line 'HIGH' when the
clock line SCL is at logic 'HIGH' (Indicating the 'STOP' condition)
79

(continued)
• First generation I2C devices were designed to support data rates
only up to 100kbps.
• Over time, there have been several additions to the specification so
that there are now five operating speed categories:
• Standard mode (Sm – Data rate up to 100kbit/sec)
• Fast mode (Fm – Data rate up to 400kbit/sec)
• Fast mode Plus (Fm+ – Data rate up to 1Mbit/sec)
• High speed mode (Hsm – Data rate up to 3.4Mbit/sec)
• Ultra Fast mode (UFm – Data rate up to 5Mbit/sec)
80

Serial Peripheral Interface (SPI) Bus
• The Serial Peripheral Interface Bus (SPI) is a synchronous bi-directional
full duplex four-wire serial interface bus.
• The concept of SPI was introduced by Motorola.
• SPI is a single master multi-slave system.
• There can be more than one masters, but only one master device can be
active at any given point of time.
• SPI requires four signal lines for communication. They are:
• Master Out Slave In (MOSI) – Signal line carrying the data from master to slave
device. It is also known as Slave Input/SIave Data In (SI/SDI)
• Master In Slave Out (MISO) – Signal line carrying the data from slave to master
device. It is also known as Slave Output (SO/SDO)
• Serial Clock (SCLK) – Signal line carrying the clock signals
• Slave Select (SS) – Signal line for slave device select. It is an active low signal
81

(continued)
• The bus interface diagram shown in the figure illustrates the
connection of master and slave devices on the SPI bus.
Fig: SPI Bus Interfacing
82

(continued)
• The master device is responsible for generating the clock signal.
• It selects the required slave device by asserting the corresponding slave
device's slave select signal 'LOW’.
• The data out line (MISO) of all the slave devices when not selected floats
at high impedance state.
• The serial data transmission through SPI bus is fully configurable.
• SPI devices contain a certain set of registers for holding these configurations.
• The control register holds the various configuration parameters like
master/slave selection for the device, baud rate selection for
communication, clock signal control, etc.
• The status register holds the status of various conditions for transmission
and reception.
83

(continued)
• SPI works on the principle of 'Shift Register’.
• The master and slave devices contain a special shift register for the data to transmit or
receive.
• The size of the shift register is device dependent. Normally it is a multiple of 8.
• During transmission from the master to slave, the data in the master's shift register is
shifted out to the MOSI pin and it enters the shift register of the slave device through
the MOSI pin of the slave device.
• At the same time the shifted out data bit from the slave device's shift register enters
the shift register of the master device through MISO pin.
• In summary, the shift registers of 'master' and 'slave' devices form a circular buffer.
• When compared to I2C, SPI bus is most suitable for applications requiring transfer of
data in 'streams'.
• The only limitation is SPI doesn't support an acknowledgement mechanism.
84

External Communication Interfaces
• External Communication Interface refers to the different
communication channels/buses used by the embedded system to
communicate with the external world.
• E.g.: RS-232 C & RS-485, Universal Serial Bus (USB), IEEE 1394
(Firewire), Infrared (IR), Bluetooth (BT), Wi-Fi, ZigBee, GPRS, etc.
85

Infrared (IrDA)
• Infrared (IrDA) is a serial, half duplex, line of sight based wireless technology
for data communication between devices.
• It is in use from the olden days of communication and you may be very familiar
with it.
• E.g.: The remote control of TV, VCD player, etc. works on Infrared.
• Infrared communication technique uses infrared waves of the electromagnetic
spectrum for transmitting the data.
• It supports point-point and point-to-multipoint communication, provided all
devices involved in the communication are within the line of sight.
• The typical communication range for IrDA lies in the range 10 cm to 1 m.
• The range can be increased by increasing the transmitting power of the IR
device.
86

Infrared (IrDA) (continued)
• IR supports data rates ranging from 9600bits/second to 16Mbps.
• Depending on the speed of data transmission IR is classified into:
• Serial IR (SIR) – supports data rates ranging from 9600bps to 115.2kbps.
• Medium IR (MIR) – supports data rates of 0.576Mbps and 1.152Mbps.
• Fast IR (FIR) – supports data rates up to 4Mbps.
• Very Fast IR (VFIR) – supports data rates up to 16Mbps.
• Ultra Fast IR (UFIR) – supports data rates up to 96Mbps.
• GigaIR – supports data rates 512 Mbps to 1 Gbps.
87

• IrDA communication involves a transmitter unit for transmitting the data
over IR and a receiver for receiving the data.
• Infrared Light Emitting Diode (LED) is the IR source for transmitter and at
the receiving end a photodiode acts as the receiver.
• Both transmitter and receiver unit will be present in each device
supporting IrDA communication for bidirectional data transfer.
• Such IR units are known as 'Transceiver’.
• Certain devices like a TV remote control always require unidirectional
communication and so they contain either the transmitter or receiver
unit.
• The remote control unit contains the transmitter unit and TV contains the
receiver unit.
88

• Infrared Data Association (IrDA ) is the regulatory body responsible for defining
and licensing the specifications for IR data communication.
• IR communication has two essential parts: a physical link part and a protocol
part.
• The physical link is responsible for the physical transmission of data between
devices supporting IR communication
• Protocol part is responsible for defining the rules of communication.
• The physical link works on the wireless principle making use of Infrared for
communication.
• The IrDA specifications include the standard for both physical link and protocol
layer.
• The IrDA control protocol contains implementations for Physical Layer (PHY),
Media Access Control (MAC) and Logical Link Control (LLC).
89

• IrDA is a popular interface for file exchange and data transfer in low
cost devices.
• IrDA was the prominent communication channel in mobile phones
before Bluetooth's existence.
90

Bluetooth (BT)
• Bluetooth is a low cost, low power, short range wireless technology for
data and voice communication.
• Bluetooth was first proposed by Ericsson in 1994.
• Bluetooth operates at 2.4GHz of the Radio Frequency spectrum and uses
the Frequency Hopping Spread Spectrum (FHSS) technique for
communication.
• Bluetooth supports a data rate of up to 1Mbps to 24Mbps and a range of
approximately 30 to 100 feet for data communication (depending on the
version)
• v1.2 supports data rate up to 1Mbps
• v2.0 + EDR supports data rate up to 3Mbps
• v3.0 + HS and v4.0 supports data rate up to 24Mbps
91

Bluetooth (BT) (continued)
• Bluetooth communication has two essential parts – a physical link
part and a protocol part.
• The physical link is responsible for the physical transmission of data
between devices supporting Bluetooth communication
• The protocol part is responsible for defining the rules of
communication.
• The physical link works on the wireless principle making use of RF
waves for communication.
• Bluetooth enabled devices essentially contain a Bluetooth wireless
radio for the transmission and reception of data.
92

• The rules governing the Bluetooth communication is implemented in the
'Bluetooth protocol stack’.
• The Bluetooth communication IC holds the stack.
• Each Bluetooth device will have a 48 bit unique identification number.
• Bluetooth communication follows packet based data transfer.
• Bluetooth supports point-to-point (device to device) and point-to-multipoint
(device to multiple device broadcasting) wireless communication.
• The point-to-point communication follows the master-slave relationship.
• A Bluetooth device can function as either master or slave.
• When a network is formed with one Bluetooth device as master and more than
one device as slaves, it is called a Piconet.
• A Piconet supports a maximum of seven slave devices.
93

• Bluetooth is the favourite choice for short range data
communication in handheld embedded devices.
• Bluetooth technology is very popular among cell phone users as
they are the easiest communication channel for transferring
ringtones, music files, pictures, media files, etc. between
neighbouring Bluetooth enabled phones.
• Bluetooth Low Energy (BLE)/Bluetooth Smart is a latest addition to
the Bluetooth technology.
• BLE allows devices to use much less power compared to the standard
Bluetooth connections, while offering most of the connectivity of
Bluetooth and maintaining a similar communication range.
94

• Bluetooth 4.2 specification enables IoT support through low-power
IP connectivity, with support for flexible Internet connectivity
options (IPv6/6LoWPAN or Bluetooth Smart Gateways) and
implements industry-leading privacy, power efficiency and industry
standard security.
95

• The Bluetooth standard specifies the minimum requirements that a
Bluetooth device must support for a specific usage scenario.
• The Generic Access Profile (GAP) defines the requirements for
detecting a Bluetooth device and establishing a connection with it.
• All other specific usage profiles are based on GAP.
• Serial Port Profile (SPP) for serial data communication, File Transfer
Profile (FTP) for file transfer between devices, Human Interface Device
(HID) for supporting human interface devices like keyboard and mouse
are examples for Bluetooth profiles.
96

• BLE implements various application specific profiles for communicating
with low power Bluetooth peripherals like fitness devices, blood
pressure and heart rate monitors, etc.
• Examples:
• Healthcare Profiles
• HTP – Health Thermometer Profile, GLP – Glucose Profile, BLP – Blood Pressure
Profile, etc.
• Sports and Fitness Profiles
• HRP – Heart Rate Profile, LNP – Location and Navigation Profile, RSCP – Running
Speed and Cadence Profile, etc.
• The specifications for Bluetooth communication is defined and licensed
by the standards body 'Bluetooth Special Interest Group (SIG)'.
97

Wi-Fi
• Wi-Fi or Wireless Fidelity is the popular wireless communication technique for
networked communication of devices.
• Wi-Fi follows the IEEE 802.11 standard.
• Wi-Fi is intended for network communication and it supports Internet Protocol
(IP) based communication.
• It is essential to have device identities in a multipoint communication to
address specific devices for data communication.
• In an IP based communication each device is identified by an IP address, which
is unique to each device on the network.
98

Wi-Fi (continued)
• Wi-Fi based communications require an intermediate agent called Wi-Fi
router/Wireless Access point to manage the communications.
• The Wi-Fi router is responsible for restricting the access to a network, assigning
IP address to devices on the network, routing data packets to the intended
devices on the network.
• Wi-Fi enabled devices contain a wireless adaptor for transmitting and receiving
data in the form of radio signals through an antenna.
• The hardware part of it is known as Wi-Fi Radio.
• Wi-Fi operates at 2.4 GHz or 5 GHz of radio spectrum and they co-exist with
other ISM band devices like Bluetooth.
99

Wi-Fi (continued)
• Figure illustrates the typical interfacing of devices in a Wi-Fi
network.
Fig: Wi-Fi Network
100

Wi-Fi (continued)
• For communicating with devices over a Wi-Fi network, the device when
its Wi-Fi radio is turned ON, searches the available Wi-Fi network in its
vicinity and lists out the Service Set Identifier (SSID) of the available
networks.
• If the network is security enabled, a password may be required to
connect to a particular SSID.
• Wi-Fi employs different security mechanisms like Wired Equivalency
Privacy (WEP), Wireless Protected Access (WPA), etc. for securing the
data communication.
• Wi-Fi supports data rates ranging from 1 Mbps to 1.73 Gbps depending
on the standards (802.11a/b/g/n/ac) and access/modulation method.
• Depending on the type of antenna and usage location (indoor/outdoor),
Wi-Fi offers a range of 100 to 1000 feet.
101

ZigBee
• ZigBee is a low power, low cost, wireless network communication protocol
based on the IEEE 802.15.4-2006 standard.
• ZigBee is targeted for low power, low data rate and secure applications for
Wireless Personal Area Networking (WPAN).
• The ZigBee specifications support a robust mesh network containing multiple
nodes.
• This networking strategy makes the network reliable by permitting messages to
travel through a number of different paths to get from one node to another.
• ZigBee operates worldwide at the unlicensed bands of Radio spectrum, mainly
at 2.400 to 2.484 GHz, 902 to 928 MHz and 868.0 to 868.6 MHz.
• ZigBee supports an operating distance of up to 100 metres and a data rate of
20 to 250 Kbps.
102

ZigBee (continued)
• In the ZigBee terminology, each ZigBee device falls under any one of the
following ZigBee device category:
• ZigBee Coordinator (ZC)/Network Coordinator
• The ZigBee coordinator acts as the root of the ZigBee network.
• The ZC is responsible for initiating the ZigBee network and it has the capability to
store information about the network.
• ZigBee Router (ZR)/Full function Device (FFD)
• Responsible for passing information from device to another device or to another
ZR.
• ZigBee End Device (ZED)/Reduced Function Device (RFD):
• End device containing ZigBee functionality for data communication.
• It can talk only with a ZR or ZC and doesn't have the capability to act as a mediator
for transferring data from one device to another.
103

ZigBee (continued)
• The diagram shown in figure gives an overview of ZC, ZED and ZR in
a ZigBee network.
Fig: A ZigBee network model
104

ZigBee (continued)
• ZigBee is primarily targeting application areas like home & industrial
automation, energy management, home control/security,
medical/patient tracking, logistics & asset tracking and sensor
networks & active RFID.
• Automatic Meter Reading (AMR), smoke detectors, wireless
telemetry, HVAC control, heating control, lighting controls,
environmental controls, etc. are examples for applications which
can make use of the ZigBee technology.
105

ZigBee (continued)
• ZigBee PRO offers full wireless mesh, low-power networking capable of
supporting more than 64,000 devices on a single network.
• It provides standardized networking designed to connect the widest range of
devices, in any industry, into a single control network.
• ZigBee PRO offers an optional new and innovative feature, ‘Green Power’ to
connect energy harvesting for self-powered devices into ZigBee PRO
networks.
• The ‘Green Power’ feature of ZigBee PRO is the most eco-friendly way to
power battery-less devices such as sensors, switches, dimmers and many
other devices and allows them to securely join ZigBee PRO networks.
• ZigBee 3.0 delivers all the features of ZigBee while unifying the ZigBee
application standards found in ZigBee devices.
• ZigBee 3.0 standard enables communication and interoperability among
devices for smart homes, connected lighting and other markets.
106

ZigBee (continued)
• The specifications for ZigBee is developed and managed by the
ZigBee Alliance, a non-profit consortium of leading semiconductor
manufacturers, technology providers, OEMs and end-users
worldwide.
107

References
1. Shibu K V, “Introduction to Embedded Systems”, Tata McGraw Hill, 2009.
2. Raj Kamal, “Embedded Systems: Architecture and Programming”, Tata
McGraw Hill, 2008.
108

Embedded Systems (18EC62) – Embedded System Components (Module 3)

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