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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
74138 74139
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