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Memory Overview

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-flop

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Memory Overview

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  1. 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-flop Memory 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 word Byte – A special term used for a group of 8 bits Nibble – 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

  2. Example… 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

  3. Example… Which memory stores the most bits: a 5M x 8bits memory OR a 1M x 16bits memory? Solution: Capacity 5M x 8 = 5 x 1,048,576 x 8 = 41,943,040 bits 1M x 16 = 1,048,576 x 16 =16,777,216 bits • The 5M x 8 memory stores more bits.

  4. MEMORY TERMINOLOGY • Density- Another term for capacity • Address – 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.

  5. MEMORY TERMINOLOGY • Density- Another term for capacity • Address – 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.

  6. 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.

  7. Memory Type RAM (Random Access Memory) ROM (Read Only Memory) 1. MROM : Mask-programmed ROM. 2. PROM : Programmable ROM 3. EPROM : Erasable PROM 4. EEPROM : Electrically-erasable PROM or EAROM: Electrical Alterable ROM 6. FLASH MEMORY 1. SRAM : Static RAM 2. DRAM : Dynamic RAM

  8. ROMREAD-ONLY MEMORIES • The 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

  9. ROM BLOCK DIAGRAM

  10. 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.

  11. 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.

  12. THE READ OPERATION • 16 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.

  13. 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.

  14. ROM TYPES OF MROM

  15. 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.

  16. ROM PROGRAMMABLE ROM (PROM)

  17. EPROM samb. ERASABLE PROGRAMMABLE ROM (EPROM) • 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 .

  18. 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

  19. ROM ERASABLE PROGRAMMABLE ROM (EPROM) Disadvantages: • They must be removed from their circuit to be erased and reprogrammed • The erase operation erases the entire chip-there is no way to select only certain addresses to be erased • The erase and reprogramming process can typically take 20 minutes or more.

  20. ROM ERASABLE PROGRAMMABLE ROM (EPROM) Fused quartz

  21. 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

  22. ROM ELECTRICALLY ERASABLE PROM (EEPROM)

  23. 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

  24. ROM example description

  25. ROM example description

  26. RAM(Random Access Memory) • 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

  27. RAM(Static Random Access Memory) SRAM CELL • SRAM use bistablelatching 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.

  28. STATIC RAM (SRAM) RAM(Static Random Access Memory) • 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.

  29. RAM(Static Random Access Memory) Cip piawai industri • 2k x 8 bit (16 kilobit) 6164/6264 8k x 8 bit (64 kilobit) 43256/66256 32k x 8 bit (256 kilobit)

  30. RAM(Static Random Access Memory)

  31. RAM(Static Random Access Memory) Pin description • A0 – An - address line • connect to address bus • D0 – 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

  32. RAM(Dynamic Random Access Memory) • 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 SRAM • The main internal memory of the most personal microcomputers uses a DRAM because of its high capacity and low power consumption

  33. RAM(Dynamic Random Access Memory) DRAM - Operation principle 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.

  34. RAM(Dynamic Random Access Memory) Principle of operation of DRAM read, for simple 4 by 4 array.

  35. Jenis-jenis DRAM RAM(Dynamic Random Access Memory) • FPM DRAM – Fast page mode DRAM membolehkan data dicapaidengancepatpada ‘page’ yang sama (beberapaalamatdalamjulattertentu) • EDO DRAM – Extended Data Output DRAM membaikiciri FPM darisegicaramembacadanmenulis data. • SDRAM – Synchronous DRAM mempunyaicirimembaca data denganlebihlaju.

  36. Different between ROM and RAM • 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

  37. Introduction to address decoding • Full address decoding • Partial address decoding • Implementing address decoders • Examples

  38. Memory Map and Address Decoding 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

  39. 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.

  40. SOLUTION • What is the entire range for system addresses? • What is the entire range for every component ROM, I/O and RAM • Assume that memory map figure like that: ROM I/O RAM unused

  41. 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) Start 0000 H ROM I/O RAM unused End FFFF H

  42. 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 0000 H ROM 2FFFF H I/O RAM unused FFFF H

  43. 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 = $3000 End Address I/O = $3000 + $1000 – 1 = $3FFF 0000 H ROM 2FFF H 3000 H I/O 3FFF H RAM unused FFFF H

  44. 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 • = $4000 • End Address for RAM = $4000 + $4000 – 1 • = $7FFF 0000 H ROM 2FFF H 3000 H I/O 3FFF H 4000 H RAM 7FFF H unused FFFF H

  45. Memory Map for the System is Figure below: 0000 2FFF 3000 3FFF 4000 7FFF 8000 FFFF ROM I/O RAM UNUSED

  46. Latihan 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

  47. Latihan 1 : • 2. Jika pemetaan alamat suatu mikropemproses 8 bit diberi seperti berikut, tentukan saiz ROM, RAM dan I/O 0000 RAM I/O UNUSED ROM 7FFF 8000 8FFF 9000 BFFF C000 FFFF

  48. 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.

  49. Untukmerekabentukpenyahkodalamat, terdapatbeberapalangkahiaitu: i. Tentukanjulatalamatuntukperanti (rujukpetaingatan) ii.   Bilangancip yang diperlukan iii.  Bilangantalianalamatpadacip (talianalamatrendahdaripemproseskecip) iv. Bakitalianalamatmasukkepenyahkodalamat v. Lukislitarpenyambunganantarakomponen- komponenberkaitan.

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