memory overview

• Memory stores the program running and the data on which the program operates•Data store in binary code.• Terminology:

Memory Cell – A device or an electrical circuit used to store a single bit (0 or 1). Ex: flip-flopMemory Word – A group of bits (cells) I memory that represents instructions or data of some type. Ex: Index Register consisting of 16 bit can be considered to be a memory wordByte – A special term used for a group of 8 bitsNibble – Half of Byte ( 4bit).Capacity –A way of specifying how many bits can be stored in a particular memory device or complete memory system. Capacity metrics unit: 1K = 210 = 1024.

1M = 220 = 1,048,576. 1G = 230 = 1,073,741,824

Memory Overview

A certain semiconductor memory chip is specified as 2K x 8. a. How many words can be stored on this chip?b. What is the word size? c. How many capacity can this chip store?

Solution: a. 2K = 2 x 1024 = 2048 location. b. Word size is 8-bits (one byte). c. The total capacity is 2048 x 8bit = 16,384 bits

Example…

Which memory stores the most bits: a 5M x 8bits memory OR a 1M x 16bits memory?

Solution: Capacity5M x 8 = 5 x 1,048,576 x 8 = 41,943,040

bits1M x 16 = 1,048,576 x 16 =16,777,216 bits

The 5M x 8 memory stores more bits.

Example…

Density- Another term for capacityAddress – A number that identifies the location of

a word in memory.Read operation – the operation whereby the

binary word stored in a specific memory location (address) is sense and then transferred to another device.

Write operation – The operation whereby a new word is placed into a particular memory location.

Access Time – A measure of memory device’s operating speed. It is the amount of time required to perform a read operation.

MEMORY TERMINOLOGY

Main Memory – Also referred to as the computer’s working memory. It stores instructions and data the CPU is currently working on. It is the highest-speed memory in the computer and is always a semiconductor memory.

Auxiliary Memory – Also referred to as mass storage because it stores massive amounts of information external to the main memory. It is slower in speed than main memory and is always nonvolatile. CDs are common auxiliary devices.

MEMORY TERMINOLOGY

Memory Type

ROM(Read Only Memory)

RAM(Random Access Memory)

1. MROM : Mask-programmed ROM.2. PROM : Programmable ROM3. EPROM : Erasable PROM4. EEPROM : Electrically-erasable PROM or EAROM: Electrical Alterable ROM6. FLASH MEMORY

1. SRAM : Static RAM2. DRAM : Dynamic RAM

ROMREAD-ONLY MEMORIESThe read-only memory is type of semiconductor

memory designed to hold data that either are permanent or will not change frequently. (Non-volatile)

During normal operation data can be read from ROM.

Data can be entered electrically –programming or burning-in the ROM.

Some ROMs cannot have their data changed once they have been programmed; others can be erased and reprogrammed as often as desired.

A major use for ROMs is in the storage of programs in microcomputers. When the microcomputer is turned on, it can immediately begin executing the program stored in ROM

ROM BLOCK DIAGRAM

Has 3 sets of signals: address inputs, control inputs, and data outputs.

Store 16 words because it has 2^4=16 possible addresses, and each word contains 8-bit because there are 8 data outputs.

This is a 16 x 8 ROM. The most common numbers of data outputs for

ROMs are 4, 8,16 bits with 8-bit word being the most common.

Control input CS-Chip Select – an enable input that enables or disabled the ROM outputs

Many ROMs have two or more control inputs that must be active in order to enable the data outputs so that data can be read from the selected address.

ROM BLOCK DIAGRAM

CS input shown in figure is active-LOW; therefore, it must be in the LOW state to enable the ROM data to appear at the data outputs

Notice that there are no R/W input because the ROM cannot be written into during normal operation.

ROM BLOCK DIAGRAM

THE READ OPERATION16 different data words are stored at the 16

different address locations.In order to read a data word from ROM, we

need to do 2 things :Apply the appropriate address inputs Activate the control inputs.Ex: if we want to read the data stored at location 0111 of the

ROM, we must apply A3A2A1A0=0111 to the address inputs and then apply a LOW to CS. The address inputs will be decoded inside the ROM to select the correct data word, 11101101, that will appear at outputs D7 to D0. If CS is kept HIGH the ROM outputs will be disabled and will be in the Hi-Z state.

TYPE OF ROM MASK PROGGRAMMED ROM(MROM)Has its storage location written into by the

manufacturer according to the customer’s specifications.

A mask is used to control the electrical interconnections on the chip.

A special mask is required for each different set of information to be stored in the ROM.

Disadvantage – of this type of ROM is that cannot be reprogrammed in the event of a design change requiring a modification of the stored data

Is the most economical approach when a large quantity of identically programmed ROMs are needed.

ROM TYPES OF MROM

ROM PROGRAMMABLE ROM (PROM)For lower-volume applications,

manfacturers have developed fusible-link PROMs that are user-programmable; that is, they are not programmed during the manufacturing process but are custom-programmed by the user.

Once programmed, cannot be erased and reprogrammed

If the programmed in the PROM must be changed, the PROM must be thrown away.

ROM PROGRAMMABLE ROM (PROM)

EPROM samb.

EPROM programing can be done by charging floating gate in side it.

The programming of an EPROM can be done in special programmer unit circuit and erasing using UV light source .

ERASABLE PROGRAMMABLE ROM (EPROM)

http://en.wikipedia.org/wiki/File:Floating_gate_transistor.png

ERASABLE PROGRAMMABLE ROM (EPROM)

Can be programmed by the user and can be erased and reprogrammed as often as desired.

Nonvolatile memory that will hold its stored data indefinitely

The programming process is usually performed by a special programming circuit that is separate from he circuit in which the EPROM will eventually be working.

EPROMs are available in a wide range of capacities and access times; devices with a capacity of 512K x 8 and can access time of 20 ns are commonplace

Disadvantages:1. They must be removed from their circuit to be

erased and reprogrammed 2. The erase operation erases the entire chip-

there is no way to select only certain addresses to be erased

3. The erase and reprogramming process can typically take 20 minutes or more.

ROM ERASABLE PROGRAMMABLE ROM (EPROM)

ROM ERASABLE PROGRAMMABLE ROM (EPROM)

Fused quartz

ROM ELECTRICALLY ERASABLE PROM (EEPROM)The disadvantages of the EPROM were overcome

by the development of the electrically erasable PROM (EEPROM) as an improvement over the EPROM.

The erasing and programming of an EPROM can be done in circuit ( without UV light source or a special programmer unit)

Advantages: ability to erase and rewrite individual bytes (8-bit words) in the memory array electrically.

During a write operation, internal circuitry automatically erases all of the cells at an address location prior to writing in the new data. This byte eras ability makes it much easier to make changes in the data stored in an EEPROM

ROM ELECTRICALLY ERASABLE PROM (EEPROM)

ROM FLASH MEMORY From EEPROM to Flash memory cell, is like the

simple singe-transistor EPROM cell, being only slightly larger.

Allows electrical erasability but can be built with much higher densities than EEPROMs.

The cost of flash memory is considerably less than for EEPROM

Rapid erase and write times.Use bulk erase operation in which all cells on the chip

are erase simultaneously This bulk erase process typically requires hundreds of

milliseconds compares to 20 minutes for UV EPROMs

ROM example description

Any memory address location is as easily accessible as any other.

Is used in computers for the temporary storage of programs and data.

The contents of many RAM address locations will be read from and written to as the computer executes a program. This requires fast read and write cycle times for the RAM so as not to slow down the computer operation

Disadvantage – it is volatile and will lose all stored information if power is interrupted or turned off.(volatile)

Advantage- can be written into and read from rapidly with equal ease

RAM(Random Access Memory)

SRAM use bistable latching circuitry for single bit storage.

Using BJT and MOS technology. Advantage of BJT is high speed

device.Advantage of CMOS is high

capacity and low power consumption.

SRAM CELL

RAM(Static Random Access Memory)

http://en.wikipedia.org/wiki/Bistable

http://en.wikipedia.org/wiki/Latch_(electronics)

http://en.wikipedia.org/wiki/File:SRAM_Cell_(6_Transistors).svg

STATIC RAM (SRAM)Can store data as long as power is applied

to the chip.SRAM memory cells are essentially flip-

flops that will stay in a given state (store a bit) indefinitely provide that power to the circuit is not interrupted.

Main applications of SRAM are used in various electronic applications including toys, automobiles, digital devices and computers.


6116 2k x 8 bit (16 kilobit)

Cip piawai industri

6164/6264 8k x 8 bit (64 kilobit)43256/66256 32k x 8 bit (256 kilobit)


Pin descriptionA0 – An - address line

connect to address busD0 – Dn - bus line

connect to bus data CS* - Chip select atau CE* - Chip enable

to active device

OE* - Output enable RAM give data to data bus

WE* - Write enable to active write data bus


High capacity, low power requirement, moderate operating speed.

DRAM stores 1s and 0s as charges on a small MOS capacitor. Because of the tendency for these charges to leak off after a period of time, DRAM require periodic recharging or the memory cells; this called refreshing the DRAM.

Have 4 times the density of SRAMThe main internal memory of the most

personal microcomputers uses a DRAM because of its high capacity and low power consumption

RAM(Dynamic Random Access Memory)

DRAM is usually arranged in a square array of one capacitor and transistor per cell.

The illustrations to the right show a simple example with only 4 by 4 cells (modern DRAM can be thousands of cells in length/width).

The long lines connecting each row are known as word lines. Each column is actually composed of two bit lines, each one connected to every other storage cell in the column.

DRAM - Operation principle


Principle of operation of DRAM read, for simple 4 by 4 array.


http://upload.wikimedia.org/wikipedia/commons/3/3d/Square_array_of_mosfet_cells_read.png

Jenis-jenis DRAM1. FPM DRAM – Fast page mode DRAM

membolehkan data dicapai dengan cepat pada ‘page’ yang sama (beberapa alamat dalam julat tertentu)

2. EDO DRAM – Extended Data Output DRAM membaiki ciri FPM dari segi cara membaca dan menulis data.

3. SDRAM – Synchronous DRAM mempunyai ciri membaca data dengan lebih laju.


ROM : Read-Only Memory Non-volatile (data retained even without power) Exists on all computers Functions on general-purpose computer: power-on self test, basic input/output system (BIOS), monitor program, etc. Functions on embedded systems: power-on self test, monitor

program, application program.

RAM : Random Access Memory Volatile (data disappears without power) Functions on general purpose computer: main memory for

running operating system and application program Functions on embedded systems: scratch-pad memory May not be required on very simple embedded systems

Different between ROM and RAM

Introduction to address decodingFull address decodingPartial address decodingImplementing address decodersExamples

Different portions of memory are used for different purposes: RAM, ROM, I/O devices

Even if all the memory was of one type, we still have to implement it using different and unique addressing.

This means that for a given valid address, one and only one memory-mapped component must be accessed.

Address decoding is the process of generating chip select (CS*) signals from the address bus for each device in the system

Memory Map and Address Decoding

Contoh :

Let’s assume a very simple system like that:> CPU 8 bit data bus line > 16 bit address bus line> 12 Kbyte ROM> 4 Kbyte for I/O ports> 16 Kbyte RAM

Make a sample memory map for that system.

i. What is the entire range for system addresses?

ii. What is the entire range for every component ROM, I/O and RAM

iii. Assume that memory map figure like that:

SOLUTION

ROM

I/O

RAM

unused

i. System Size = 2n (n= address pin)= 216= 65536 Byte

Start Address = 0 End Address = 65536 – 1 (size -1)

= 65535

Range Address System : 0 -- 65535 OR 0000 - FFFF (hexadecimal)

ROM

I/O

RAM

unused

0000 H

FFFF H

Start

End

ii. Range Address for ROM

Given Size of ROM = 12 Kbyte= 12 x 1024 byte

= 12288 byte= 3000 (hex)

> Start Address for ROM = 0000 > End Address for ROM = 3000 – 1

= 2FFF

ROM

I/O

RAM

unused

0000 H

FFFF H

2FFFF H

iii. Range Address for I/O

Given Size of I/O = 4 Kbyte= 4 x 1024 byte= 4096 byte= $1000 (hex)

Start Address I/O = End Address for ROM + 1 = $2FFF + 1

= $3000End Address I/O = $3000 + $1000 – 1

= $3FFF ROM

I/O

RAM

unused

0000 H

FFFF H

2FFF H3000 H

3FFF H

iv. Range Address for RAM

Given Size of RAM = 16 Kbyte= 16 x 1024 byte= 16384 byte= $4000

Start Address for RAM = End Address for I/O + 1 = $3FFF + 1

= $4000End Address for RAM = $4000 + $4000 – 1

= $7FFFROM

I/O

RAM

unused

0000 H

FFFF H

2FFF H3000 H

3FFF H4000 H

7FFF H

Memory Map for the System is Figure below:

0000

2FFF3000

3FFF4000

7FFF8000

FFFF

ROM

I/O

RAM

UNUSED

Latihan 1 :

1. Lukiskan pemetaan alamat suatu sistem mikropemproses 68000. Spesifikasi luaran adalah seperti berikut :

- EPROM bersaiz 2 MB bermula dari alamat $000000- RAM bersaiz 4MB berakhir di alamat $7FFFFF- I/O bersaiz 256 KB bermula dari alamat $800000

2. Jika pemetaan alamat suatu mikropemproses 8 bit diberi seperti berikut, tentukan saiz ROM, RAM dan I/O

RAM

I/O

UNUSED

ROM

0000

FFFF

80008FFF9000

BFFFC000

7FFF

Latihan 1 :

Penyahkod Alamat Dalam suatu sistem komputer, terdapat

beberapa peranti yang berada di bawah kawalan pemproses.

Pada satu masa, pemproses hanya boleh bertukar data atau berinteraksi hanya dengan satu peranti sahaja.

Pemilihan peranti ditentukan oleh kedudukannya dalam peta ingatan. Jadi penyahkod alamat (address decoder) diperlukan bagi memilih peranti yang hendak diaktifkan.

i. Tentukan julat alamat untuk peranti (rujuk peta ingatan)

ii. Bilangan cip yang diperlukaniii. Bilangan talian alamat pada cip (talian

alamat rendah dari pemproses ke cip)iv. Baki talian alamat masuk ke penyahkod

alamatv. Lukis litar penyambungan antara komponen-

komponen berkaitan.

Untuk merekabentuk penyahkod alamat, terdapat beberapa langkah iaitu :

RAM

Contoh :Lukiskan sambungan penyahkod alamat bagi suatu sistem komputer yang mempunyai kapasiti ingatan 256 x 4 bit. Diberi satu cip ingatan RAM 64 x 4 bit dan peta ingatan seperti berikut :

terdapat 256 ruang alamat

Peta Ingatan

00

FF

1) Bilangan cip = saiz sistem saiz cip

= 256 x 4 = 4 cip RAM 64 x 42) Talian alamat sistem : 2n = 256 n = log 256 = 8 talian alamat sistem (A0 – A7)

log 2 3) Talian alamat cip :

2n = 64 n = log 64 log 2

= 6 talian iaitu A0 – A5 ( talian alamat rendah dari pemproses terus ke cip ingatan )

4) Baki talian = 8 – 6 = 2 iaitu A6 dan A7 (masukan ke penyahkod alamat)

5. Penyambungan litar penyahkod alamat adalah seperti berikut :

D0-D3

Penerangan

Talian teratas A6 dan A7 disambungkan ke penyahkod alamat. Litar penyahkod berfungsi memilih satu daripada 4 cip ingatan tersebut.

Penyahkod yang digunakan adalah ‘ 2- line to 4 - line’

Setiap cip mempunyai CS input masing-masing. Jika A6 dan A7 berlogik ‘0’, maka pin CS0 akan aktif iaitu logic ‘0’ .

Ini bermakna RAM 1 akan dipilih. Lokasi ingatan yang digunakan antara

setiap cip ingatan ditentukan oleh talian A0 hingga A5.

Susunan lokasi yang dipanggil pemetaan alamat adalah seperti berikut :

Kaedah untuk menentukan talian yang masuk ke cip dan baki talian yang masuk ke penyahkod

Disamping itu terdapat satu lagi kaedah untuk menentukan talian yang masuk ke cip dan baki talian yang masuk ke penyahkod alamat iaitu dengan merujuk kepada peta ingatan.

Alamat mula ROM 1 = $ 00 0 0 0 0 0 0 0 0Alamat akhir ROM 1 = $ 3F 0 0 1 1 1 1 1 1

Mula dari kanan :Bit yang bernilai 0 di alamat mula dan 1 di alamat akhir pergi terus ke ingatan.

Di sini A0 hingga A5 pergi terus ke ingatan. Baki talian iaitu A6 – A7 pergi ke penyahkod.

Perhatikan nilai-nilai A6 - A7 dimana setiap cip mempunyai nilai yang berbeza dan nilai ini yang menentukan cip yang akan diaktifkan.

Latihan 2:

1. Kirakan jumlah cip EPROM 27128 bersaiz 16K x 8 bit yang diperlukan bagi suatu sistem komputer 64K x 8 bit. Lukis sambungan penyahkod alamat bagi sistem ingatan tersebut.

2. Kirakan jumlah cip RAM 2114 bersaiz 1024 x 4 bit yang diperlukan bagi suatu sistem komputer 3K x 8 bit. Lukis sambungan penyahkod alamat bagi sistem ingatan tersebut.

memory overview

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