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ECE 353Introduction to Microprocessor Systems
Michael J. Schulte
Week 9
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Administrative MattersQuiz #2 is Thursday, April 10th from 7:15 to 8:30 PM Covers modules 3 and 4 (weeks 5-8, hw 3, 4)
Readings for week 9 Textbook 7.5, 9 ADUC 9-10, 33-36, 43-47, 79-82
Discussion section tonight Review for Quiz #2 Problems post on course webpage
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TopicsMemory technologiesOrganization and operation of typical SRAM, EPROM and flash memory devicesMemory subsystem designAddress decoder implementationSRAM timing characteristics
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Memory TerminologyHow could we classify memory devices?Read-Only Memory (ROM) In common usage, it is memory that is
nonvolatile.
Random-Access Memory (RAM) The time required to access any
memory location is the same – it does not need to be accessed in any order.
In common usage, it is memory that can be read or written with equal ease.
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Memory TechnologiesROM (non-volatile) Masked ROM Field programmable
EPROM OTP PROM (fuse or EPROM)
Electrically erasable EEPROM (or E2PROM) Flash memory
RAM (volatile) SRAM DRAM Pseudo-SRAM
Emerging memory technologies
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Memory OrganizationLogical organization Organization as seen looking at the
device from the outside Linear array of registers (memory
locations)
Physical organization Different physical organizations can be
used to implement the same logical organization
Physical organization affects performance and cost
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SRAM InterfacesRAM with 3 control inputs /CS, /OE, /WE Read Write
RAM with 2 control inputs /CS, /WE (or R/W)
/CS
/WE
/OE
internal write signal
internal read signal
/CS
/WEinternal write signal
internal read signal
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SRAM OrganizationLogical Organization Typically 1, 4 , 8 or 16 bit widths
Physical Organization Rectangular bit array Two-level decoding (row and column) Characteristic delays and timing requirements are
specified in memory devices datasheet (Example)
NV-SRAM Uses an alternate power source to maintain SRAM
when system power is off Requires logic to switch power sources and
prevent spurious writes during power-up/power-down
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EPROMElectrically programmable, non-volatileRequires UV light to erase Quartz window in package
Floating polysilicon gate avalanche injection MOS transistor (FAMOS) Operation
Programmer loads device out-of-circuitOTP EPROMs eliminate quartz windowEEPROMs are electrically erasable Byte-erasable / writeable Low-density
JEDEC Packages
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Flash MemoryActually Flash EEPROM, commonly just called flash memoryCharacteristics Technologies Endurance Blocking, programming and erasing
Applications ROM replacement GP NV-RAM Solid-state disk (flash-disk) Example
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Memory Subsystem Design
Memory banks Increasing memory width Increasing memory depth Increasing memory width and depth
Address decoding Boundaries
If address is a 2m boundary, then what is the result of (address AND (2m-1))?
We normally decode memory devices to be aligned on boundaries at least as large as they are
Exhaustive (full) vs. partial (reduced) decoding
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Memory ArchitecturesWide (n-byte) buses Addressing effects Byte transfer support
Data lanes Control signals
Bus resizing Static Configurable Dynamic
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Memory Subsystems Review
What is the purpose of an address decoder circuit, and where does its output usually get connected?What is exhaustive decoding, and what effects does it have?What is partial decoding, and what effects does it have?
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SRAM Timing Characteristics
An SRAM device has key timing parameters specified for the read cycle. tAA – address access time
tRDHA – data valid after address changes tACS – chip select access time
tRHCS – data valid after chip select tCHZ – time until device floats bus after chip select dis-
asserted tOE – output enable access time
tOHZ – time until device floats bus after output enable dis-asserted
tRC – read cycle time
The write cycle has a complementary set of specifications.
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Sample Timing Diagram
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7C1046SRAM
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27C512EPROM
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HM624100HCSRAM
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SRAM Timing Compatibility
In order to ensure that we will be able to reliably read and write the memory device, we need to ensure that the processor system bus interface is compatible with the memory device.This is accomplished by analyzing the timing for all relevant parameters of both the processor and memory, and ensuring that the operations can be completed reliably.
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Wrapping UpQuiz #2 will be held Thursday 4/10/2008 at 7:15-8:30pm Covers educational objectives for
modules 3 and 4 (weeks 5 through 8) Single 3x5 card with original handwritten
notes No calculators Instruction set references and any
needed datasheets will be provided
Reading for next week Supplement #3, review chapter 9 in text
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Physical Memory Organization
32K x 8 SRAM
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FAMOS Gate Operation
Programming
Erasing
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JEDEC
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Flash Blocks
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Flash Memory Application:Disk-on-Key
Up to 4GB nonvolatile storageNo battery or power supply
Specifications:Data retention up to 10 years Erase cycles: 1,000,000 times Shock resistance: 1000 G (maximum)
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RAM Read – 3 control signals
/CS
Dx
Ax
/OE
/WE
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RAM Write – 3 control signals
/CS
Dx
Ax
/OE
/WE
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Increasing Memory Depth
CE
A0
A15 D7
D0
CE
A0
A14 D7
D0
CE
A0
A14 D7
D0
Extending Depth
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Increasing Memory Width
CE
A0
A15 D7
D0
CE
A0
A15 D3
D0
CE
A0
A15 D3
D0
Extending Width
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Increasing Memory Depth & Width
CE
A0
A15 D7
D0CE
A0
A14 D3D0
Extending Width and Depth
CE
A0
A14 D3D0
CE
A0
A14 D3D0
CE
A0
A14 D3D0