MEMORY SYSTEM DESIGN

Identify the types of memory chip and their functions

Define the difference between exhaustive and partial address decoder

Design address decoder using exhaustive and partial technique

ROM (Read-Only Memory)• containing permanent or semi-

permanent data• ROM is non-volatile; even after turn off

supply, the contents of ROM will remain

• Used to store a program• Types available in market

ROM (Read-Only Memory) PROM (Programmable ROM) EPROM (Erasable PROM) EEPROM (Electrically EPROM)

ROM Block Diagram

RAM (Random Access Memory)• containing none permanent data• RAM is volatile, so data stored in RAM stays

there only as long the supply is turn on• Used to store a temporary data• Types available in market

SRAM (Static RAM) DRAM (Dynamic RAM) EDORAM (Extended Data Output RAM) BEDORAM (Burst EDORAM) SDRAM (Synchronous DRAM) DDR-DRAM (Double Data Rate-Synchronous DRAM)

RAM Block Diagram

WHY?• uP has too many device connected using

bus system• Only one device can active or

communicate with uP in one time Functions

• Monitor the state of address bus and determine when the memory chip should be enabled

Before• Must know how much memory is needed• Calculate how many address line need to

be used to locate memory Begin

• Draw memory map• Find the address range for every

component Find based address Find end address

End Add = Based Add + Component (memory) Size -1

Add Line = log (Memory Size) log 2

• Draw address decoding table

• Draw address decoder Full address decoding technique Partial address decoding technique

Device

Address Range

Address

Address lineA15 – A12

A11 – A8

A7 – A4 A3 – A0

First

Last

Exhaustive Decoding• All address lines must be used to access

each physical memory location, either to access data or activate selected device

Partial Decoding• Not all the address lines available

for address decoding take part in decoding process

• Simplest and least expensive• Normally used decoder chips

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