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Static Memory

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Static Memory

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Static Memory Systems Those semiconductor components in a

microcomputer that store the program and data.

Role in the system can be seen as passive – memory simply stores to information and except for specialized architectures, performs no operation on the data stored there.

Today it is common to have yyG bytes in a system.

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Static RAM Characteristics Forms the bulk of memory in a system. Is read/write memory. For read/write memory have choice of

Static RAM Dynamic RAM

Special Characteristic Memory ROM (PROM, EPROM, EEPROM) EEPROM partially used as RAM Computational Memory

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Static RAM Nonvolatile – as long as power is on value is retained

with no other action.

Data

Select

Data*

GND

Vcc

NMOS Memory cell

Data

Select

Data*

GND

Vcc

CMOS Memory cell

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Gate Equivalent

Data

Select

Data*

GND

Vcc

CMOS Memory cell

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1st approach to 16K of RAM

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2nd approach to 16K of RAM

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Internals of 6264LP Static CMOS RAM

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A RAM Chip 6264LP-10 -10 means

100ns access time

Consider all parameters

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Bus Contention Read after read to same chip Must consider what happens in preceding

cycle and what happens in next cycle Must also consider read after write, write after

read, and write after write timing Timing for the same chip and for different

chips

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Read cycle bus contention

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Write cycle bus contention

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PROM and EPROM Programmable Read Only Memory

One time programmable Electrically Programmable Read Only

Memory Programmed by provided a higher than normal

programming voltage – 12V to 25V UV erasable

Used to program and code startup code – the bios in a PC

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PROM and EPROMS Come in many sizes Byte wide is very common Wordwide is also common

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EEPROM Another form of non-volatile memory Read cycle is like other PROMs Write cycle timing is long – typically over

100 us.

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EEPROMs and flash EEPROMs Flash EEPROMs are similar to electrical

erasable PROMs

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Example of flash EEPROM use Flash

EEPROMs are similar to electrically erasable PROMs