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1
MEMORIES
2
MEMORIES
Devices that store digital information
Represented in terms of bit, byte, nibble, KB,MB etc
Consists of arrays of storage elements (latches, flip-flops or capacitors)
Memories are made up of arrays of cells (cell can store either 1 or 0)
Location specified by a row and a column is called Address of unit of data
...
of words * word size
no
...
of words or address locations
N =word size
4
CLASSIFICATION OF MEMORIES
Depends upon speed, capacity, units of transfer, volatile/non-volatile,
erasable/non-erasable
The memory unit is an essential
component in any digital
computer since it is needed for
storing programs and data
SPEED
Not all accumulated information COST/BIT
is needed by the CPU at the same
time
Therefore, it is more economical
to use low-cost storage devices to
serve as a backup for storing the
information that is not currently
used by CPU
CAPACITY
5
CLASSIFICATION OF MEMORIES
The memory unit that directly communicate with CPU is called the main memory
Devices that provide backup storage are called auxiliary memory
The memory hierarchy system consists of all storage devices employed in a computer
system from the slow by high-capacity auxiliary memory to a relatively faster main
memory, to an even smaller and faster cache memory
The main memory occupies a central position by being able to communicate directly
with the CPU and with auxiliary memory devices through an I/O processor
A special very-high-speed memory called cache is used to increase the speed of
processing by making current programs and data available to the CPU at a rapid rate
6
GENERAL STORAGE METHOD
READ-WRITE OPERATION
Data entered into memory during write operation and data comes out of
memory during read operation from data bus
...
Binary code used for representing desired address on address bus, are
decoded internally and appropriate address is selected
...
Address decoder decodes the address and select specified location in memory
...
When write command executes, data from data bus is placed in selected memory
address
...
Address decoder decodes the address and select specified location in memory
...
8X8 Byte Organized Memory Array
ADDRESS REGISTER
DATA REGISTER
100
3x8
Address Decoder
1
0
0
1
1
0
1
1
DATA BUS
10011011
ADDRESS BUS
9
TYPES OF MEMORIES
RAM:
It is a volatile (data storage temporary ie
...
First data bit written into memory is first to be read out
...
LIFO
Last in first out
Last data to be stored is first to be retrieved
...
14
FLASH MEMORIES
High density read/write and random access memories
...
Non volatility
...
Comparatively fast operation
...
Used in floppy, Hard disk in laptops
...
15
COMPARISON
Memory Type
Non Volatile
High Density
One Transistor
Cell
In-System
Writability
Flash
YES
YES
YES
YES
SRAM
NO
NO
NO
YES
DRAM
NO
YES
YES
YES
ROM
YES
YES
YES
NO
EPROM
YES
YES
YES
NO
EEPROM
YES
NO
NO
YES
16
PROGRAMMABLE LOGICAL DEVICES
17
PROGRAMMABLE LOGICAL DEVICES
Devices in which the logic function is programmed by the user and in some cases can be
reprogrammed many times
...
Consumes less area than fixed function logic device
Can be designed and changed without rewiring or replacing components and are faster
than fixed one
...
Can replace fixed function SSI or MSI devices and their interconnections
1
...
PROM (Programmable Read Only Memory)
20
TYPES OF PLDs----Continued
2
...
(Product ROM and Sum ROM)
Consists of
array
Programmable array is a grid of conductors that form rows and columns with a
fusible link at each cross point
...
Programmed by the user in the field not the manufacturer
Logical functions determined by the absence or presence of connections at
fixed pre-defined positions
Similar to PROM but differ in their internal structure ie
...
PLA (Programmable Logic Array) also called FPLA (Field PLA)
22
TYPES OF PLDs----Continued
3
...
PAL (Programmable Array Logic)
24
TYPES OF PLDs----Continued
4
...
Consists of reprogrammable AND array and a fixed OR array with
programmable output configurations ( these are two difference between PAL and
GAL)
Uses E 2CMOS (Electrically Erasable CMOS) technology instead of Bipolar
technology and fusible links
25
TYPES OF PLDs----Continued
4
...
Difference between FPGA: FPGA has absence of on chip non volatile memory and CPLD is used to load
configuration data for an FPGA from non volatile memory, CPLD is based on sea of gates (SOP) whereas
FPGA based on Look up tables
27
TYPES OF PLDs----Continued
CPLDs (Complex Programmable Logic Devices)
28
TYPES OF PLDs----Continued
FPGAs (Field Programmable Gate Arrays)
Based on gate array technology
Uses a grid of logic gates, similar to that of an ordinary gate array called logical blocks but programming is
done by customer not by the manufacturer, in the field outside the factory
...
WHY SILICON IN IC?
Easily available
Cheap
High temperature bearer
Easy to fabricate
...
1
...
Medium Scale Integration (MSI)
Fixed function ICs that contains 10 to 100 equivalent gate circuits (hundreds of
transistors) on each chip
Include encoders, decoders, counters, registers, multiplexers, arithmetic circuits
etc
33
LEVELS OF INTEGRATION
3
...
Very Large Scale Integration (VLSI)
Fixed function ICs that contains 10000 to 100000 equivalent gate circuits (hundreds
of thousands of transistors) on each chip
Include 1 MB RAM, second generation and later microprocessors chips etc
5
...
MOSFET
The transistors BJT and MOSFET are both useful for amplification and switching applications
...
BJT
MOSFET
Bipolar Junction Transistor
Metal Oxide Semiconductor Field-Effect Transistor
BJT has an emitter, collector and base
MOSFET has a gate, source and drain
Preferred for low current applications like for switching
purposes for instance, simply because they are cheaper
Preferred for high power functions
In digital and analog circuits, MOSFETs are considered to be
more commonly used than BJTs these days as they handle
power more efficiently
The operation of BJT is dependent on the current at the base
...
so CMOS has the advantage over
NMOS/PMOS
40
COMPLEMENTARY METAL OXIDE SEMICONDUCTOR (CMOS)
Based on MOS technology (Combination of NMOS and PMOS)
Used in LSI, VLSI and ULSI circuits
Highest packing density so compact circuit fabrication ie
...
3V power supply required) and can vary over a wide
range than TTL (2-6V for CMOS to 4
...
5V for TTL)
Least power dissipation
High speed operation
High noise immunity
Sensitive to ESD(Electrostatic Discharge)
41
SUMMARY
Logical Specifications
I2L
ECL
TTL
CMOS
Power supply
required
1V
5 to 32V
4
...
5V
3V
So, Better is I2L, CMOS, then TTL and then ECL as per operating voltage
Propagation Delay
Noise Immunity
TTL > I2L > CMOS >= ECL
so, fastest is ECL, CMOS then I2L and lastly TTL
Low
Poor
Good
Highest
Packing Density
High
Higher than TTL but
lower than I2L,
CMOS
Less
Highest
Power Dissipation
Less
High
High
least
Sensitive to ESD
No
No
No
Yes
Technology
BJT
BJT
BJT
MOS
42
DIGITAL DISPLAYS
43
DIGITAL DISPLAY
A display that gives the information in the form of characters (numbers or letters)
A display device is an output device for presentation of information in visual or tactile
form (the latter used for example in tactile electronic displays for blind people)
When the input information is supplied as an electrical signal, the display is called
an electronic display
...
44
SEGMENT DISPLAY
Some displays can show only digits or alphanumeric characters
...
The segments are usually single LEDs or liquid crystals
...
There are several types:
Seven-segment display (most common, digits only)
Fourteen-segment display
Sixteen-segment display
45
SEVEN SEGMENT DISPLAY
Hexadecimal encodings for displaying the digits 0 to F
Digit
a
b
c
d
e
f
g
0
on
on
on
on
on
on
off
1
off
on
on
off
off
off
off
2
on
on
off
on
on
off
on
3
on
on
on
on
off
off
on
4
off
on
on
off
off
on
on
5
on
off
on
on
off
on
on
6
on
off
on
on
on
on
on
7
on
on
on
off
off
off
off
8
on
on
on
on
on
on
on
9
on
on
on
on
off
on
on
A
on
on
on
off
on
on
on
b
off
off
on
on
on
on
on
C
on
off
off
on
on
on
off
d
off
on
on
on
on
off
on
E
on
off
off
on
on
on
on
F
on
off
off
off
on
on
on
Digital display generally used to display numbers
but can display certain alphabets too
...
Common cathode is active high display and
Common anode is active low
Widely used in digital clocks, electronic meters,
and other electronic devices for displaying
numerical information
46
FOURTEEN SEGMENT DISPLAY
Referred to as a starburst display or a "Union Jack" display
Display based on 14 segments that can be turned on or off to produce letters and numerals
Having an additional four diagonal and two vertical segments with the middle horizontal
segment broken in half
...
DVMs display the measured voltage using LCDs or LEDs to display the result in a
floating point format
...
Obviously, if voltage measurements are taken and the results are displayed digitally with
LED or LCD displays, the instrument has to contain an A/D converter
...
Liquid crystals do not emit light directly
...
Its low electrical power
consumption enables it to be used in battery powered electronic equipment
...
Used in a wide range of applications including computer monitors, televisions, instrument
panels, aircraft cockpit displays, signage, consumer devices such as video players, gaming
51
devices, clocks, watches, calculators, and telephones,
LED DISPLAY
Diode such that light emitted at a p-n junction is proportional to the bias current; color
depends on the material used
Flat panel display, which uses light-emitting diodes as a video display
...
They are typically used outdoors in store signs and billboards and sometimes used as form
of lighting, for the purpose of general illumination, task lighting, or even stage lighting rather
than display
...
Are called "plasma" displays because the technology utilizes small cells containing
electrically charged ionized gases, or what are in essence chambers more commonly
known as fluorescent lamps
...
Screen burn in is a problem associated with Plasma displays
...
Plasma monitors display images
using phosphors
...
SIZE AND COST
Least cost compared to
other two
Edge-LED monitors are
thinner than standard LCD;
Costly as compared to LCD
Higher size and hence costly
POWER CONSUMPTION
High
Save up to 30%-40% power
than a LCD monitor of same
size
30% more higher than LCD
PLAYING FAST MOVING
VIDEOS (RESPONSE
TIME)
Contrast levels are good but
Between LCD and Plasma
not as led and plasma, so poor
Contrast levels are way higher
than any other displays, so good
56
DIFFERENCES
LCD DISPLAY
LED DISPLAY
PLASMA DISPLAY
SCREEN BURN IN/ NO
GHOSTING
LED monitors are softer on the eyes compared
to LCD monitors which makes them the right
choice for people who work for long hours on
their computers
Yes but temporary
PICTURE QUALITY Have to maintain a viewing
angle of 30o to see the
picture properly but has
good contrast and
brightness making it
suitable for any situation, so
advantageous than plasma
for long hours
Improved brightness and contrast levels than Viewing angle is greater
lcd,
than other two but not
Provides a better overall picture clarity,
so apt for computer
resolution and finer colors than lcd,
working for long hours
Get the same picture quality even when
viewed from different angles;
LED monitors offer more intense lighting than
cold cathode fluorescent lamps