Transcript ECE 301 – Digital Electronics

ECE 301 – Digital Electronics
Memory
(Lecture #21)
Memory
Memory is required to store:
1. data
2. application programs
3. operating system
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Memory
Can be broadly classified as:
Random Access Memory (RAM)
or
Read Only Memory (ROM)
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Random Access Memory (RAM)

Can be written to or read from.



Reading from RAM is non-destructive.
Access time to read from any memory
location is the same.


Read/Write memory
As compared to serial access memory.
Volatile

Information is lost when power is
removed.
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Random Access Memory (RAM)
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Random Access Memory (RAM)


Static Random Access Memory (SRAM)

Based on the Flip-Flop

Requires a large number of transistors

Fast
Dynamic Random Access Memory (DRAM)

Uses a single transistor to store charge

Requires very few transistors

Must be periodically refreshed

Slow(er)
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Random Access Memory (RAM)
What is typically stored in RAM?
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Read Only Memory (ROM)

Can only be read from.

Memory is written (or “programmed”) once

Reading from ROM is non-destructive.

Access time to read from any memory
location is the same.


As compared to serial access memory.
Non-Volatile

Information is retained even after power
is removed.
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Read Only Memory (ROM)
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Read Only Memory (ROM)

Programmable Read Only Memory (PROM)


Erasable PROM (EPROM)


Can be “programmed” and erased
Electrically Erasable PROM (EEPROM)


Can be “programmed”
Can be erased using an electrical signal
UV Erasable PROM (UVEPROM)

Can be erased using Ultraviolet light
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Read Only Memory (ROM)
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Read Only Memory (ROM)
What is typically stored in ROM?
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Memory
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Memory
Random Access Memory
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Random Access Memory


Address

Location in memory of the binary information

Must be decoded to select the appropriate
location and read/write the associated data

k-bit address → 2k memory locations
Data

Binary information of interest

Stored in a specific location in the memory

Typically organized into words

Each word has n bits
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Random Access Memory
address
data
10-bit address
1024 locations
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Random Access Memory

Read


Indicates that the memory is to be read
Write

Indicates that the memory is to be written
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Random Access Memory
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Random Access Memory



Rather than use the Read and Write
signals, most commercially available RAM
chips use Enable and Read/Write'
Enable

Used to enable the selected RAM chip

Aka. “chip select”
Read/Write'

RAM is read when Read/Write' = 1

RAM is written when Read/Write' = 0
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Random Access Memory
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Random Access Memory
Write Cycle
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Random Access Memory
Read Cycle
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Random Access Memory
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Random Access Memory
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Acknowledgments
The slides used in this lecture were taken, with permission,
from those provided by Pearson Prentice Hall for
Digital Design (4th Edition).
They are the property of and are copyrighted by
Pearson Education.
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