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Title: Memories
Description: detailed about memories

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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
Title: Memories
Description: detailed about memories