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Embedded Computing System(06CS74)

UNIT - 2
INTRODUCTION TO EMBEDDED SYSTEMS – 2, DEVICES - 1:
Formalization of system design
Design process and design examples
Classification of embedded systems
Skills required for an embedded system designer. I/O types and examples
Serial communication devices; Parallel device ports
Sophisticated interfacing features in device ports.
6 Hours

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Embedded Computing System(06CS74)

Formalization of system design
Design process in embedded system
Abstraction
Each problem component first abstracted. For example, Display picture and text as an abstract
class Robotic system problem abstraction in terms of control of motors in different degrees of
freedoms. Application software abstracted as concurrently running multiple threads and interrupt
service threads.
Program Model
Procedure Oriented , Objected Oriented , Sequential processes, Concurrent processes , State
machine.
Object oriented Model Object oriented Model:- Classes , Objects , Interfaces, Package
Hardware and Software architecture
Assumed to consists multiple layers , Each architectural layer be well understood before a design
.
Extra functional Properties Extra functional Properties
Extra functionalities required in the system being developed be well understood from the design.
System Related Family designs
Families of related systems developed earlier taken into consideration during designing
Modular Design
Decomposition of software into modules that are to be implemented. Modules should be such
that they can be composed (coupled or integrated) later. Effective Modular design should ensure
effective (i) function independence, (ii) cohesion and (iii) coupling.
Modules: Be clearly understood and maintain continuity. Appropriate protection strategies are
necessary for each module. A module is not permitted to change or modify another module
functionality. For example, protection from a device driver modifying the configuration of
another device

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Embedded Computing System(06CS74)
Mapping : Mapping into various representations done considering the software requirements.
For example, data flow in the same path during the program flow can be mapped together as a
single entity.
Transform and transaction mapping Transform and transaction mapping For example, an
image is input data to a system; it can have a different number of pixels and colors of each pixel.
The system has to store or process each pixel and color Transform mapping of image is done by
appropriate compression and storage algorithms. Transaction mapping is done to define the
sequence of the images

Software tools used in the design
i> Editor:

ii>Interpreter

iii>Complier

iv>Assembler

v>Simulator

vi>source code engg software.

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Embedded Computing System(06CS74)

vii>Locator

viii> Trace scope

A charge pump is a kind of DC to DC converter that uses capacitors as energy storage elements
to create either a higher or lower voltage power source. Charge pump circuits are capable of high
efficiencies, sometimes as high as 90-95% while being electrically simple circuits.
Charge pumps use some form of switching device(s) to control the connection of voltages to the
capacitor. For instance, to generate a higher voltage, the first stage involves the capacitor being
connected across a voltage and charged up. In the second stage, the capacitor is disconnected
from the original charging voltage and reconnected with its negative terminal to the original
positive charging voltage. Because the capacitor retains the voltage across it (ignoring leakage
effects) the positive terminal voltage is added to the original, effectively doubling the voltage.
The pulsing nature of the higher voltage output is typically smoothed by the use of an output
capacitor.
This is the charge pumping action, which typically operates at tens of kilohertz up to several
megahertz to minimize the amount of capacitance required. The capacitor used as the charge
pump is typically known as the "flying capacitor".
i)
ii)
iii)

clock oscillator circuit
system timer
power up reset and watch dogtimer

i)ans)clock oscillator circuit
The clock controls the time for executing an instruction .after the power supply, the clock
basic unit of a system. a processor needs a clock oscillator circuit. The clock controls the
various clocking requirements of a system the cpu of the system timers and the cpu machine
cycles are for fetching codes and the data forms memory and then decoding and executing
them at the processor and for transferring the result to memory.

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Embedded Computing System(06CS74)
ii)system timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an
event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed
time, a timer counts down from a specified time interval, like an hourglass. Timers can be
mechanical, electromechanical, electronic (quartz), or even software as all modern computers
include digital timers of one kind or another. When the set period expires some timers simply
indicate so (e.g., by an audible signal), while others operate electrical switches.
iii)power up reset and watch dog timer
A power-up reset generator is a microcontroller or microprocessor peripheral that generates a
reset signal when power is applied to the device. It ensures that the device starts operating in a
known state.
In VLSI devices, the power-up reset is an electronic device incorporated into the integrated
circuit that detects the power applied to the chip and generates a reset impulse that goes to the
entire circuit placing it into a known state. A simple PUR is composed by an RC device that
charges with the rising of the supply voltage. A schmitt trigger is used so that the rising charged
voltage of the RC network generates an impulse. This impulse is generated based on the two
threshold voltages of the schmitt trigger. When the input voltage at the schmitt trigger coming
from the RC network reaches the first threshold voltage the output of the schmitt trigger switches
so that it generates the first edge of the input. The charging of the RC network should be long
enough so that the PUR can reset all the internal circuits before the charging voltage reaches the
other threshold voltage of the schmitt trigger and the output to switch back.
One of the issues with using RC network to generate power up reset pulse is the sensitivity of the
R and C values to the power-supply ramp characteristics. When the power supply ramp is rapid,
the R and C values can be calculated so that the time to reach the switching threshold of the
schmitt trigger is enough to apply a long enough reset pulse. When the power supply ramp itself
is slow, the RC network tends to get charged up along with the power-supply ramp up. So when
the input schmitt stage is all powered up and ready, the input voltage from the RC network
would already have crossed the schmitt trigger point. This means that there might not be a reset
pulse supplied to the core of the VLSI.
A watchdog timer (or computer operating properly (COP) timer) is a computer hardware or
software timer that triggers a system reset or other corrective action if the main program, due to
some fault condition, such as a hang, neglects to regularly service the watchdog (writing a
"service pulse" to it, also referred to as "kicking the dog", ―
petting the dog‖, "feeding the
[1]
watchdog" or "waking the watchdog"). The intention is to bring the system back from the
nonresponsive state into normal operation.
Watchdog timers can be more complex, attempting to save debug information onto a persistent
medium; i.e. information useful for debugging the problem that caused the fault. In this case a
second, simpler, watchdog timer ensures that if the first watchdog timer does not report
completion of its information saving task within a certain amount of time, the system will reset
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Embedded Computing System(06CS74)
with or without the information saved. The most common use of watchdog timers is in embedded
systems, where this specialized timer is often a built-in unit of a microcontroller.
Even more complex watchdog timers may be used to run untrusted code in a sandbox.[2]
Watchdog timers may also trigger fail-safe control systems to move into a safety state, such as
turning off motors, high-voltage electrical outputs, and other potentially dangerous subsystems
until the fault is cleared.

Classification of embedded systems

Skills required for an embedded system designer. I/O types and examples

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Embedded Computing System(06CS74)

Serial communication devices
Data Communication is one of the most challenging fields today as far as technology
development is concerned. Data, essentially meaning information coded in digital form, that is, 0s
and 1s, is needed to be sent from one point to the other either directly or through a network.
And when many such systems need to share the same information or different information through
the same medium, there arises a need for proper organization (rather, ―
socialization‖) of the whole
network of the systems, so that the whole system works in a cohesive fashion.

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Embedded Computing System(06CS74)
Therefore, in order for a proper interaction between the data transmitter (the device needing to
commence data communication) and the data receiver (the system which has to receive the data sent
by a transmitter) there has to be some set of rules or (―
protocols‖) which all the interested parties
must obey.
The requirement above finally paves the way for some DATA COMMUNICATION STANDARDS.
Depending on the requirement of applications, one has to choose the type of communication strategy.
There are basically two major classifications, namely SERIAL and PARALLEL, each with its
variants. The discussion about serial communication will be undertaken in this lesson.

Any data communication standard comprises
• The protocol.
• Signal/data/port specifications for the devices or additional electronic circuitry
involved.

What is Serial Communication? (home…..)
Serial data communication strategies and, standards are used in situations having a limitation of the
number of lines that can be spared for communication. This is the primary mode of transfer in longdistance communication. But it is also the situation in embedded systems where various subsystems
share the communication channel and the speed is not a very critical issue.
Standards incorporate both the software and hardware aspects of the system while buses mainly
define the cable characteristics for the same communication type.
Serial data communication is the most common low-level protocol for communicating between two
or more devices. Normally, one device is a computer, while the other device can be a modem, a
printer, another computer, or a scientific instrument such as an oscilloscope or a function generator.
As the name suggests, the serial port sends and receives bytes of information, rather characters (used
in the other modes of communication), in a serial fashion - one bit at a time. These bytes are
transmitted using either a binary (numerical) format or a text format.
All the data communication systems follow some specific set of standards defined for their
communication capabilities so that the systems are not Vendor specific but for each system the user
has the advantage of selecting the device and interface according to his own choice of make and
range.

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Embedded Computing System(06CS74)
The most common serial communication system protocols can be studied under the following
categories: Asynchronous, Synchronous and Bit-Synchronous communication standards.

Asynchronous Communication and Standards (home…..)
The Protocol
• This protocol allows bits of information to be transmitted between two devices at an arbitrary
point of time.
• The protocol defines that the data, more appropriately a ―
character‖ is sent as ―
frames‖ which in
turn is a collection of bits.
• The start of a frame is identified according to a START bit(s) and a STOP bit(s) identifies the
end of data frame. Thus, the START and the STOP bits are part of the frame being sent or
received.
• The protocol assumes that both the transmitter and the receiver are configured in the same way,
i.e., follow the same definitions for the start, stop and the actual data bits.
• Both devices, namely, the transmitter and the receiver, need to communicate at an agreed upon
data rate (baud rate) such as 19,200 KB/s or 115,200 KB/s.
• This protocol has been in use for 15 years and is used to connect PC peripherals such as
modems and the applications include the classic Internet dial-up modem systems.
• Asynchronous systems allow a number of variations including the number of bits in a
character (5, 6, 7 or 8 bits), the number of stops bits used (1, 1.5 or 2) and an optional parity
bit. Today the most common standard has 8 bit characters, with 1 stop bit and no parity and
this is frequently abbreviated as '8-1-n'. A single 8-bit character, therefore, consists of 10 bits
on the line, i.e., One Start bit, Eight Data bits and One Stop bit (as shown in the figure
below).
• Most important observation here is that the individual characters are framed (unlike all the
other standards of serial communication) and NO CLOCK data is communicated between the
two ends.

The Typical Data Format (known as “FRAME”) for Asynchronous Communication

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