Download 02 Memory and Registered

Memory and Register
Memory
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terminology
read/write operation
volotile/non volatile
determine the capacity from input and output
timing requirements of ROM and EEPROM and
Flash memory
• RAM and its organization
• Memory combinding
Memory layout in computer
• high-speed memory for internal
• low speed for external storage
Terminology
• Cell : electrical circuit used to store a single bit data such as flip-flop
circuit
• Word: compound of bits
• Byte: 8 bits word
• Nibble: 4 bits word, half a byte
• Capacity:
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describe how many bits can store in a memory module
often show in (number of word x word size) form
1K of cell = 210 = 1024 cells
1M or cell = 220
1G or cell = 230
• Volatile memory
• type or memory that always require electrical power unless data will lost.
General memory signal and diagram
• address lines corporate with address bus
• data line corporate with data bus
• control lines for memory operation type
• R/-W read write operation, active low
• ME : memory enable, active low
• to enable the memory module
• other name
• /CS chip select
• /CE chip enable
• /OE : Output Enable : used to enable the RAM data to
Data BUS
ROM – Read Only Memory
• designed : holding permanent data / not change
frequently
• Data may enter during manufacturing process
• Store microcomputer program because it is not
volatile
• also programmed and data such as calculator,
appliances, security system etc.
ROM block diagram
ROM architecture
• 4 basic part
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row decoder
column decoder
register array
output buffer
Type of ROM
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Mask-Programmed ROM
Programmable ROM (PROM)
Erasable Programmable ROM (EPROM)
Electrically Erasable PROM (EEPROM)
Flash Memory
Mask-Programmed ROM
• program are written by manufacturer for custom
specification
• use photographic negative as mask to control
electrically interconnection
• mask is expensive thus need large quantity for
economical cost
• Cannot be reprogrammed
• example use: ROM character generator for CRT
PROM
• fusible-link MROM
• custom programmed
by user
• OTP (One Time
Programmable)
properties: Once
programmed, it cannot
be erase.
Erasable Programmable ROM (EPROM)
• When Program
• need special voltage (typically 10-25V)
• used amount time (typically 50 msec)
• Erasable: by Ultraviolet (UV) light
• examples
• 2732 : 4K x 8 NMOS EPROM
• 2764 : 8K x 8
Electrically Erasable PROM (EEPROM)
• Erase by Electrically (high voltage) eg. 21v
generated from 5v
• Write faster than PROM (5usec)
• During Write, internal circuitry
automatically erases the cell
• Former from Intel ex. 2816, 2864
EEPROM symbol
Flash memory
• high density than EEPROM
• Faster erase and write time than EEPROM
• 2 mode of erase
• bulk erase: erase all cell
• sector erase: specified part of cell to erase e.g.
512 bytes
• typical 10 usec write time
• example 28F256A
Flash memory example
ROM applications
• Firmware
• data and program code while power up
• Data table
• constant data for look-up eg. store
trigonometric tables
• data converter
• input one type output with another eg. input
BCD code output with 7-segment code
ROM application-data converter
Auxiliary Storage
• Because of competitively cost some note
book use as a small secondary storage
• eg. thumb drive
RAM-Random Access Memory
• Read/Write able memory
• Volatile thus used as temporary storage or
as registers
• 2 kinds when divided by technology
• Static RAM – Semiconductor RAM
• Dynamic RAM – Capacitor RAM
• size step from bytes, 1K, 2K, 4K…
RAM architecture
RAM operation step
• Set the address code at address bus
• Activate /CS (Chip Select)
• When Write
• set Data to Data bus
• R/-W set low
• When Read
• R/-w set high
• Data comes out to data bus
• /OE
Read cycle
Write cycle
Static RAM timing
Dynamic RAM
• structure visualized as an array of single-bit cell
Each cell representation
• data often referred the capacity to 1 cell e.g.
4096K x 1 for 1 bit word size, equals to
1024Kx4 (1Meg x 4) for 4 bit word size.
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Address Multiplexing
• Owing to its capacity is high, the require a
lot of address lines
• Multiplexing circuit is used to decrease
number of address lines
• add more control signal lines
• CAS : Column Address Strobe
• RAS : Row Address Strobe
Refreshing
• Each memory cell has to be refresh periodically
(typically 4 ms) or the data will be lost
• Refresh performs when Read operation
• By activate the ROW signal address, thus need
more external or built in circuit
• 2 refreshing mode
• burst mode: normal operation is suspended, refresh
contiguous row
• distributed mode
• intersperse with normal operation
• when refresh
• RAS is activate
• CAS and R/-W are high
word size expanding
• add more equal in size RAM module
Capacity expanding
• need address select signal
• often use the high+1 address line
Combining chips
• need decoder, use the higher addresses line as decode signals