Natnal School of Autonomous Systems Technologies

ioSecond Year Engineering

Module
Introduction to Autonomous Systems 1

Chapter 7
Introduction to Memory
Second Year Engineering

Dr Yasmine GUERBAI
E mail:y.guerbai@outlook.com
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 Memory is the faculty of the brain by which data or information is
encoded, stored, and retrieved when needed.

01

Text

010 111
100 100
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 Memory is the faculty of the brain by which data or
information is encoded, stored, and retrieved when needed."
— Wikipedia

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 Fequency= 2Ghz
Time =1/Frequency
2GHZ
=1/ 2*10 9
=
1/2 *10 -9
=1/2 nsec

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Memory Units Conversion Table

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Conversion Rules (based on powers of 2)

• 1 KB = 2¹⁰ = 1,024 bytes

• 1 MB = 2²⁰ = 1,048,576 bytes

• 1 GB = 2³⁰ = 1,073,741,824 bytes

• 1 TB = 2⁴⁰ = 1,099,511,627,776 bytes

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Random Acess Memory
(RAM)

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Dynamic Random Acess Memory
DRAM

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Dynamic Random Acess Memory
DRAM

Statistic Random Acess Memory

DRAM

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 Memory

Optical Memory
Magnetic Memory Semiconductor Memory

CD Hard Disk RAM

DVD Floppy Disk USB Flash Drive

Cassette Tape ROM

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 Semiconductor memories are devices used for storing digital
information. They are used in all types of devices, including
microprocessors, and also in the implementation of programmable
logic circuits.

Address
Inputs

Control
Inputs

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 Semiconductor Memories
Non-Volatile Memories
(also called Dead Memories)
ROM Volatile Memories
Read-Only Memory Random Access Memory

Non-volatile memory: these memories retain information even in the

absence of electrical power.
Volatile memory: these are memories whose data integrity is
guaranteed only when they are electrically powered. They are
readable and writable.
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Memory address Capacity

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Addres
s Address Bus
Inputs
Role: Carries the address of the memory cell (or I/O device)
where data will be read from or written to.

Example: If the CPU wants to access data at address 0x1A3F,

Control that address is sent via the address bus.
Inputs

Data Bus
Control Bus
•Role: Transfers actual data between the CPU, memory, and
Role: Carries control signals used to coordinate and manage peripheral devices.
the operations of the computer system (e.g., read/write
operations, interrupts). •Width: The size (e.g., 8, 16, 32, or 64 bits) determines how
much data can be transferred at once.
Common signals: Read, Write, Clock, Reset, Interrupt

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Exercise 1

Calculate the memory capacity?

Solution

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 Memory cell.

Exercise 2
Determine the number of
address lines in the bus?

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Basic operations on memory

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Addressing
Addressing is the process of accessing a specified
location in memory. Since memory stores binary
data, the data must be placed in memory, and it
must be copied from memory when needed.

Writing and Reading

The write operation places data at a specified
address in memory, and the read operation copies
data from a specified address in memory.
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adress(CPU)

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Cycle Time
A read or write operation is performed through the following steps:

•Selecting the address;

•Choosing between read and write (signal level applied to R/W);

•Selecting the circuit (signal level applied to CS);

•Reading or writing the data.

The combination of these operations forms a read or write cycle.

Timing diagrams show the access time ta and the cycle time tc.
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21
Types of Memory

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 Semiconductor Memories
Non-Volatile Memories
(also called Dead Memories) Volatile Memories
ROM RAM
Read-Only Memory Random Access Memory

Non-volatile memory: these memories retain information even in the

absence of electrical power.
Volatile memory: these are memories whose data integrity is
guaranteed only when they are electrically powered. They are
readable and writable.
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 Static RAM (SRAM)
All SRAMs are characterized by flip-flop memory cells. As long as a constant current is applied
to a static memory cell, it can retain a 1 or 0 state indefinitely. If the power supply is cut off, the
stored data bit is lost.

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27
Data Outputs 28
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Synchronous SRAM
Unlike asynchronous SRAM, synchronous SRAM is
synchronized with the system clock.

For example, in a computer system, synchronous

SRAM operates with the same clock signal that drives
the microprocessor, so that both the microprocessor
and the memory are synchronized for faster operation.

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A basic functional diagram of synchronous SRAM with burst mode

This memory is called

cache memory in CPU

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Exercise Memory Size Extension
• Design a 16×8 (bit) memory using 16×4 memory modules

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Exercise

1.Design a 2048×8 (bits) memory using 256×8 memory modules.

2. We want to store the information 00111111 11111011 in memory module no. 7

starting from the first line. What is the appropriate address in hexadecimal?

3. Create a table showing the address ranges in hexadecimal for each memory module.

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Dynamic memory cells
Dynamic memory cells store a single bit of data in a small capacitor rather than in a
latch.
The advantage of this type of cell is that it is very simple, allowing the construction
of very large memory arrays on a chip at a lower cost per bit.
The drawback is that the storage capacitor cannot retain its charge for a long period
of time and will lose the stored bit unless its charge is periodically refreshed.
This refreshing process requires additional memory circuitry and complicates the
operation of DRAM.
The figure shows a typical DRAM cell, consisting of a single MOS transistor and a
capacitor.

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Write 1 into a memory cell

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 Types of ROM memory
Masked ROM is generally referred to simply as ROM. It is permanently

programmed during the manufacturing process to provide widely used

standard functions, such as popular data conversions, or to deliver

functions specified by the user.

Once the memory is programmed, it can no longer be modified.

Most ROM ICs use the presence or absence of a transistor connection

at a row/column junction to represent a 1 or a 0

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38
Representation of a ROM
programmed as a binary-to-Gray
code converter.

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 PROM memory type
Programmable ROMs (PROMs) are fundamentally
the same as mask ROMs once they have been
programmed.

As you have learned, ROMs are a type of

programmable logic device.
The difference is that PROMs are delivered
unprogrammed by the manufacturer, and they can be
programmed once to meet the user’s specific needs.

A PROM uses a certain fuse programming process to

store bits, where a memory link is either blown or left
intact to represent a 0 or a 1.
The fusing process is irreversible: once a PROM is
programmed, it cannot be modified.
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EEPROM
An Electrically Erasable Programmable ROM can be both
erased and programmed using electrical pulses.
Since it can be both written and erased electrically, the
EEPROM can be quickly reprogrammed and erased
in-circuit for reprogramming.
Two types of EEPROMs are floating-gate MOS and
Metal-Nitride-Oxide-Silicon (MNOS).
Applying a voltage to the control gate in the floating-gate
structure allows the storage and removal of charges from
the floating gate.
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UV EPROM
You can recognize a UV EPROM device by the transparent UV
window on its package.
The isolated gate in the FET of a ultraviolet EPROM “floats”
inside an oxide-insulated material.
The programming process removes electrons from the floating
gate.
Erasing is done by exposing the memory chip to high-intensity
ultraviolet radiation through the transparent window at the top of
the package.
The positive charge stored on the gate is neutralized after a few
minutes to an hour of exposure. 42
 CHARACTERISTICS OF MEMORIES
 Volatility
o Volatile {RAM}
o Non-volatile {ROM, Flash memory}

 Mutability

o Read/Write {RAM, HDD, SSD, RAM, Cache, Registers…}

o Read Only {Optical ROM (CD/DVD…), Semiconductor ROM}

 Accessibility

o Random Access {RAM, Cache}

o Direct Access {HDD, Optical Disks}
o Sequential Access {Magnetic Tapes}
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