12/14/2014

1

Data Handling, Communication &

Standards (A further look)

311 - Computer Systems Engineering

Rukshan Siriwardhane

I

m

a

g

e

t

a

k

e

n

f

r

o

m

:

w

w

w

.

s

k

a

d

a

t

e

.

c

o

m

Computer Bus Systems

What is a Computer Bus? a set of physical connections which can be

shared by multiple hardware components in order to communicate with one another.

the metaphor of a "data highway" is sometimes used.

Read further on:http://en.kioskea.net/contents/375-what-is-a-computer-bus2

Bus Systems Uni directional

E.g. Address bus Bi Directional

E.g. Data bus, Control Bus TriState/Three State busA three-state bus is a computer bus connected to multiple tri-state output devices, only one of which can be enabled at any point to avoid bus contention. This scheme allows for the same bus to be shared among multiple devices.Read more on tri-state buffer at:http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/CompOrg/tristate.html

3

VMEbus (VersaModular Eurocard bus) A bus standard, originally developed for the Motorola

68000 line of CPUs Used in traffic control systems, weapons control systems,

telecommunication switching systems, data acquisition, video imaging, and robots

Ideal for harsh environments withstand shock, vibration, and extended temperatures

Read more at: http://whatis.techtarget.com/definition/VMEbus-VersaModular-Eurocard-bus

4

12/14/2014

2

IEEE 796/ multibus The Multibus standard was originally

developed by Intel. It specified four busses the Multibus System Bus the I/O Expansion Bus (iSBX) the Execution Bus (iLBX) the Multichannel I/O Bus.The multibus system bus was adopted as IEEE 796, and the iSBX bus was adopted as IEEE P959.

5

IEEE 796/ multibus Multibus is an asynchronous bus that accommodates

devices with various transfer rates while maintaining maximum throughput.

It had 20 address lines so it could address up to 1 Mb of Multibus memory and 1 Mb of I/O locations.

Multibus supported multi-master functionality that allowed it to share the Multibus with multiple processors and other DMA devices.

6

Bus Systems Bus ArbitrationQuestion: 1a) Explain what is meant by bus arbitration.b) Describe different categories of bus arbitration

7

Bus Systems Bus ArbitrationThe process used to determine which device should be in control of the bus. In systems with more than one master device, bus arbitration is required. Bus arbitration schemes must provide priority to certain master devices and, at the same time, make sure the lower priority devices are nit starved out.Bus arbitration schemes fall into four categories.

8

12/14/2014

3

Bus Systems

9

Daisy chain: Uses a grant bus control line that is passed down the bus from the highest priority device to the lowest priority device. Fairness is not ensured and it is possible that low priority devices are starved out and never allowed to use the bus. Simple but not fair.

Centralized parallel: Each device has a request control line to the bus and a centralized arbiter selects who gets the bus. Bottlenecks can result using this.

Distributed using self-detection:Similar to centralized arbitration but instead of a central authority selecting who gets the bus the devices themselves determine who has the highest priority and who gets the bus.

Distributed using collision-detection: Each device is allowed to make a request for the bus . If the bus detects any collisions, the device must make another request. (e.g. Ethernet)

InterruptsQuestion: 2Describe using diagrams how an interrupt is serviced in a computer.

10

Interrupts Vectored InterruptsI/O interrupts that tell the interrupts handler that a request for attention from an I/O device has been received and also identifies the device that sent the request.

Polled InterruptsI/O interrupt that notifies the interrupt handler that a device is ready to be handled (read or otherwise) but does not indicate which device. The interrupt controller must poll (send a signal out to) each device to determine which one made the request.

11

Interrupts Priority LevelsThe interrupt priority defines which of a set of pending interrupts is serviced first. There are 4 classes of priorities for bus interrupts. Other interrupt priorities are reserved for base kernel.A device's interrupt priority is selected based on two criteria: its maximum interrupt latency requirements and the device driver's interrupt execution time. If an interrupt is not serviced in this latency, some event is lost or serious performance degradations occur.

Read more on interrupts at:http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=%2Fcom.ibm.aix.kernelext%2Fdoc%2Fkernextc%2Finterrupts.htm

12

12/14/2014

4

Computer Peripherals

Characteristics and Operating Principles

http://www.lintech.org/comp-per/index.html

13

Data Acquisition Systems

Products and/or processes used to collect information to document or analyze some phenomenon. In the simplest form, a person logging the

temperature of an oven on a piece of paper

14

Data Acquisition Systems

With the use of electronic equipment, these types of processes have been simplified and made more accurate, versatile, and reliable.

Equipment used range from simple recorders to sophisticated computer systems.

Data acquisition products tie together a wide variety of products sensors that indicate temperature, flow, level, or pressure.

15

Data Acquisition Systems

16 Extracted from: http://www.omega.com/techref/pdf/dasintro.pdf

12/14/2014

5

Data Acquisition Systems

Analog-to-digital converter (ADC)An electronic device that converts analog signals to an equivalent digital form. The analog-to-digital converter is the heart of most data acquisition systems.

17

Analog to Digital Converter (ADC) World is not a digital environment of absolutes. The

electrical signals of the real world are not made of logical highs and lows, or zeros and ones. These signals are analog and measurable within a range of voltages or currents.

Consider a simple voltage-input ADC.

18

ADCVRef

VINDigital Output

Analog to Digital Converter (ADC) The reference voltage is the maximum value that the

ADC can convert. Our example 8-bit ADC can convert values from 0V to the reference voltage. This voltage range is divided into 256 values, or steps.The size of the step is given by: VRef / 256

e.g. For a 5V reference, the step size is:5V/256 = 0.0195V or 19.5mV

19

Analog to Digital Converter (ADC) The most significant bit of above 8-bitword indicates

whether the input voltage is greater than half the reference (2.5V, with a 5V reference). Each succeeding bit represents half the range of the previous bit.

20

Bit: Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0Volts: 2.5 1.25 0.625 0.3125 0.156 0.078 0.039 0.0195Output Value:

0 0 1 0 1 1 0 0

Adding the voltages corresponding to each set bit in 0010 1100, we get:.625 + .156 + .078 = .859 volts

12/14/2014

6

Analog to Digital Converter (ADC) The resolution of an ADC is determined by the

reference input and by the word width. The resolution defines the smallest voltage change that can be measured by the ADC.

As mentioned earlier, the resolution is the same as the smallest step size, and can be calculated by dividing the reference voltage by the number of possible conversion values. In our above example, the resolution is 19.5mV.

i.e. any input voltage below 19.5mV will result in an output of 0.Input voltages between 19.5mV and 39mV will result in an output of 1. Between 39mV and 58.6mV, the output will be 2.21

Resolution can be improved by Reducing the reference input.

Limitation..? Using an ADC with more bits.

Types of ADCs Flash ADC Successive approximation converter Sigma-deltaRead more at:

http://www.eetimes.com/document.asp?doc_id=1276974

22

Analog to Digital Converter (ADC)

The digital data may originate from a microprocessor, application-specific integrated circuit (ASIC), or FPGA (field-programmable gate array), but at some point requires conversion to an analog signal to have impact on the real world. Whether the system uses an audio amplifier, an LED

indicator, or a motor driver, the final signal will be analog in nature.

23

Digital to Analog Converter (DAC)

24

Digital to Analog Converter (DAC)

12/14/2014

7

The diagram shown is a 4-bit parallel-input DAC With a 4-bit DAC, there are 24= 16 possible input data codes as shown on the table first column.

DACs have an analog reference (VREF), along with power supply (VA), and an analog output.

In many cases, the reference and supply voltages may be the same, and therefore the DAC will have a single pin for both functions. Also, the reference can be a voltage or a current, depending on DAC design.

25

Digital to Analog Converter (DAC) The DAC multiplies the input data code by the

reference to generate the analog output. So the DAC is the opposite function of ADC, which is

a divider to convert an analog input into digital bits. The DAC can have a voltage or current output,

depending on design. Current output DACs are well suited for high frequency applications and in applications that may require more precision.

26

Digital to Analog Converter (DAC)

Consider the diagram above is a voltage-output DACThe Least Significant Bit (LSB) is the rightmost bit of the data code and represents the smallest value in a digital code and the Most Significant Bit (MSB) is the leftmost bit of the data code and also represents the half-scale value.

As you can see on the table, the LSB (0001b) represents 0.3125 V. The LSB value is determined by the basic equation below:

27

Digital to Analog Converter (DAC) The LSB value is determined by:

LSB Value = G x VREF / 2N ; G = Gain = 1 for an ideal DAC The basic transfer function:

DAC Output = G x DIN VREF / 2N

With a DIN of 1111, the DAC output = 1 x 15 x 5 / 24= 4.6875 V

28

Digital to Analog Converter (DAC)

12/14/2014

8

29

Digital to Analog Converter (DAC) Monotocity

the condition in which the DAC transfer functions slope does not change Resolution

refers to number of bits, and with the analog reference, determines granularity of the signal conversion. Resolution also refers to the output value representing one LSB.

Settling Time the time from a change in the input code until the DAC output signal is

generated and remains within specified output range. Read more at:

http://www.analog-eetimes.com/en/bridging-the-divide-part-1-dac-introduction.html?cmp_id=71&news_id=222900832

30

Digital to Analog Converter (DAC)

Data Acquisition Systems - Contd. Differential Input

Refers to the way a signal is wired to a data acquisition device.

General Purpose Interface Bus (GPIB)Synonymous with HPIB (for Hewlett-Packard), the standard bus used for controlling electronic instruments with a computer. Also called IEEE 488 in reference to defining ANSI/IEEE standards.

ResolutionThe smallest signal increment that can be detected by a data acquisition system. Resolution can be expressed in bits, in proportions, or in percent of full scale

31

Data Acquisition Systems - Contd. RS232

A standard for serial communications found in many data acquistion systems. This is the most common serial communication. only supports communication to one device connected to the bus at a

time, transmission distances up to 50 feet. RS485

Another standard for serial communications.- Not as popular as RS232, supports communication to more than one device on the bus at a time, supports transmission distances of approximately 5,000 feet.

32

12/14/2014

9

Data Acquisition Systems - Contd. Sample Rate

The speed at which a data acquisition system collects data. The speed is normally expressed in samples per second. For multi-channel data acquisition devices the sample rate is typically given as the speed of the analog-to-digital converter(A/D).

Single-ended Input (SE):Refers to the way a signal is wired to a data acquisition device. In single-ended wiring, each analog input has a unique high connection but all channels share a common ground connection.

Read more at: http://www.omega.com/prodinfo/dataacquisition.html33

Computer Interfaces

Interface Requirements To communicate between two different systems Hardware/Software/Human-Computer

Read: The Best Computer Interfaces: Past, Present, and Future http://www.technologyreview.com/news/412880/the-best-computer-interfaces-past-present-and-future/

34

Computer Interfaces

Command lineThis is a text-based interface. There is usually a "prompt" from the operating system signifying that it is ready for a command from the user. In DOS, the prompt is usually "C:>" ( ), where C: indicates the default drive (the drive that will be used unless the user changes it), and > indicating to type the command to the right. Note that this means that the user must know the correct command, and spell it correctly.

35

Computer Interfaces

Command line The computer does not display what it can do; instead,

the user must know the commands. To get the computer to do something, the user types in

the name of the appropriate command. Just the command is not enough; the computer does

nothing until the command is entered with the key.

If the command is mistyped the computer may not be very helpful.

36

12/14/2014

10

Computer Interfaces

GUI Graphical User Interface The computer displays actions and files using

letters/menus and icons. To get the computer to do something, the user

selects the words or icons. This requires only that the user know what s/he wants to do when face-to-face with it, and an icon can hint at what the computer will do when activated.

37

Computer Interfaces Agent-based interface

The software agent is a virtual assistant Suggests/asks/reminds what to do Takes commands, executes them, reports back

with results E.g. Siri in iOS

Read more on Usability: http://www.usabilitypost.com/2009/04/15/8-characteristics-of-successful-user-interfaces/

38

Computer Interfaces

Programmable Interfaces Interfaces that can be configured to get the desired

functionality by the user May be Software or Hardware

Setting up a router, Timer on a pedestal fan

39

Computer Interfaces

40

12/14/2014

11

Real-time computing (RTC) Hardware and software systems that are subject

to a real-time constraint e.g. operational deadlines from event to system

response. (airplane engine failure, anti-lock brakes) Real-time programs must guarantee response within

strict time constraints Real-time responses are often understood to be in the

order of milliseconds, and sometimes microseconds.

41

Real-time computing (RTC)Real-time systems, and their deadlines, are classified by the consequence of missing a deadline. Hard

Missing a deadline is a total system failure. (e.g. pacemakers, car engine control)

Firm Infrequent deadline misses are tolerable, but may degrade the system's

quality of service. The usefulness of a result is zero after its deadline. Soft

The usefulness of a result degrades after its deadline, thereby degrading the system's quality of service. (live video feeds, updating flight plans)42

Real-time computing (RTC)Real-time systems should not be misunderstood with high-performance systems Recommended Reading: Wikipedia article

http://en.wikipedia.org/wiki/Real-time_computing

43

X.25 X.25 is an ITU-T standard protocol suite

for packet switched wide area network (WAN) communication.

X.25 has been, to a large extent, replaced by less complex protocols, especially the IP

Recommended Reading: Wikipedia articlehttp://en.wikipedia.org/wiki/X.25

44

12/14/2014

12

Token Bus Token bus is a network implementing the token

ring protocol over a "virtual ring" on a coaxial cable. A token is passed around the network nodes and only the

node possessing the token may transmit. If a node doesn't have anything to send, the token is passed on to the next node on the virtual ring. Each node must know the address of its neighbor in the ring, so a special protocol is needed to notify the other nodes of connections to, and disconnections from, the ring.

45

Token Bus If a node doesn't have anything to send, the token is

passed on to the next node on the virtual ring. Each node must know the address of its neighbor in the ring, so a special protocol is needed to notify the other nodes of connections to, and disconnections from, the ring.

46

Channel access method

Find out on: Frequency Division Multiple Access (FDMA) Time division multiple access (TDMA) Packet mode multiple-access Code division multiple access (CDMA)/Spread

spectrum multiple access (SSMA) Space division multiple access (SDMA)

47

Modems A modem (modulator-demodulator) is a device that modulates

an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.48

12/14/2014

13

Network Operating Systems An operating system implemented orienting to facilitate

computer networking. i.e. Software that enhances a basic operating system by adding networking features E.g. OS that runs on a server and enables the server to manage

data, users, groups, security, applications, and other networking functions.A Network OS is designed to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.

Example NOSs: Unix/Linux, Mac OS X Server, Netware, Windows

49

Network Operating Systems Recommended Readings

http://developer.juniper.net/shared/jdn/docs/white_papers/JunosSDK_WhitePaper_JunosOS.pdf

http://computernetworkingnotes.com/comptia-n-plus-study-guide/network-operating-systems.html

50

Question 3a) Convert the following signed decimal numbers to twos

complement numbersI. 79II. -1345III.-67

b) Convert the IEEE 32 bit floating point number 7665000016 to decimal

c) Convert 39887.562510 to IEEE 32-bit floating point format

51

Question 4a) What is meant by

I. Micro-kernal architectures II. Monolithic kernel architectures

b) Explain 3 operating system services.c) Describe the tasks of following programming tools

I. AssemblersII. Link EditorIII. DLL

52

12/14/2014

14

Question 5a) What are the phases of Program Compilation? Explain

providing examples.

53 54

The End