9/20/6 Lecture 14 - Static Memory 1

Static Memory
9/20/6 Lecture 14 - Static Memory 2

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.
9/20/6 Lecture 14 - Static Memory 3

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
9/20/6 Lecture 14 - Static Memory 4

Static RAM
 Nonvolatile – as long as power is on value is retained with no other action.
NMOS Memory cell
CMOS Memory cell
Select
Select
Vcc
Vcc
GND
GND
9/20/6
Data
Data*
Data
Lecture 14 - Static Memory
Data*
5

Gate Equivalent
CMOS Memory cell
Vcc
Select
9/20/6
Data
GND
Lecture 14 - Static Memory
Data*
6

1 st approach to 16K of RAM
9/20/6 Lecture 14 - Static Memory 7

2 nd approach to 16K of RAM
9/20/6 Lecture 14 - Static Memory 8

Internals of 6264LP Static CMOS
RAM
9/20/6 Lecture 14 - Static Memory 9

A RAM Chip
 6264LP-10
 -10 means
100ns access time
 Consider all parameters
9/20/6 Lecture 14 - Static Memory 10

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
9/20/6 Lecture 14 - Static Memory 11

Read cycle bus contention
9/20/6 Lecture 14 - Static Memory 12

Write cycle bus contention
9/20/6 Lecture 14 - Static Memory 13

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
9/20/6 Lecture 14 - Static Memory 14

PROM and EPROMS
 Come in many sizes
 Byte wide is very common
 Wordwide is also common
9/20/6 Lecture 14 - Static Memory 15

EEPROM
 Another form of non-volatile memory
 Read cycle is like other PROMs
 Write cycle timing is long – typically over
100 us.
9/20/6 Lecture 14 - Static Memory 16

EEPROMs and flash EEPROMs
 Flash EEPROMs are similar to electrical erasable PROMs
9/20/6 Lecture 14 - Static Memory 17

Example of flash EEPROM use
 Flash
EEPROMs are similar to electrically erasable
PROMs
9/20/6 Lecture 14 - Static Memory 18