chapter 16 semiconductor, magnetic and optical memory william kleitz digital electronics with vhdl,...

Chapter 16

Semiconductor, Magnetic and Optical Memory

William KleitzDigital Electronics with VHDL, Quartus® II Version

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

Memory Concepts

• Memory locations have memory addresses

• Data are the memory contents

• 8 bits known as a byte

• See Figure 16-2 - Logic Diagram

• See Figure 16-3 - Timing Requirements




Figure 16-2




Figure 16-3




Static RAMs

• Random-Access Memory

• Read/Write Memory

• Temporary storage of data

• User can access data at any location randomly

• CD player or Hard Disk

• Static or DynamicWilliam KleitzDigital Electronics with VHDL, Quartus® II Version



Static RAMs

• Static– use flip-flops as basic storage elements

• Dynamic– use capacitors as basic storage elements– need additional refresh circuitry– can be densely packed– lower cost per bit




Static RAMs

• The 2147H Static MOS RAM– 4096 memory locations

• 4K = 4 x 1024

– each location can contain 1 bit– 4096 unique addresses

• needs 212 = 4096 address lines

– A0 to A5 identify rows

– A6 to A11 identify columnsWilliam KleitzDigital Electronics with VHDL, Quartus® II Version



Static RAMs

• The 2147H Static MOS RAM– row and column circuitry pinpoint the memory

cell– Row Select– Column Select– uses three-state buffers– See Figure 16-6

• read cycle

• write cycle




Figure 16-6




Static RAMs

• Memory Expansion– using multiple chips to get more memory capacity– See Figure 16-7 - eight 4K chips




Figure 16-7




Dynamic RAMs

• Require more support circuitry

• More difficult to use

• Less expensive per bit

• Higher density, minimizing circuit-board area

• Usually multiplex address lines

• Capacitor refreshed during refresh cycleWilliam KleitzDigital Electronics with VHDL, Quartus® II Version



Dynamic RAMs

• Refresh cycle timing– usually every 2 ms or sooner

• Dynamic RAM Controllers– developed to simplify the tasks– Intel 3243– See Figure 16-12




Figure 16-12




Read-Only Memories• Store data on a permanent basis

• Nonvolatile

• EPROM– erasable-programmable-read-only memory

• Stores– operating systems– table look-ups– language compilers




Read-Only Memories

• Mask ROMs– one-time fee to design a unique mask– very inexpensive after one-time fee

• Fusible-Link PROMs– avoid one-time fee– every memory cell has a fusible link– burned open to permanently store data– PROM programmer or MDS




Read-Only Memories

• EPROMs– can change the memory contents– expose an open window to ultraviolet light– slowest erasure time

• EEPROMs– non-volatile– erased while still in circuit– individual bits erased




Read-Only Memories• Flash Memory

– faster access times– erase entire blocks quickly– digital cameras and PDAs

• Floating-gate MOSFET used– charge remains on gate for 10 years

• OTP (one-time-programming)

• Timing requirements must be metWilliam KleitzDigital Electronics with VHDL, Quartus® II Version



Read-Only Memories

• See Table 16-4– Summary of Semiconductor Memory

• See Figure 16-19– read cycle– write cycle




Figure 16-19




Memory Expansion and Address Decoding Applications

• Address Decoding– to identify which IC is to be read or written to– See Figure 16-20

• 16K-byte EPROM (4 x 4K)

• A PROM Look-Up Table– See Application 16-1

• A Digital LCD Thermometer– See Application 16-2




Figure 16-20




Figure 16-23




Magnetic and Optical Storage

• Electro-mechanical in nature

• Non-volatile

• Magnetic– north-south or south-north polarities

• Optical– pits and lands read by a laser system

• Slower and bulkier but less expensive and higher storage capacities





• Magnetic Memory; The Floppy Disk and Hard Disk– magnetizable medium– rigid plastic jacket– Floppy

• 300 rpm• two read/write heads (one each side)• 1.44 MB• removable• transfer rates of 45KB/sec





• Magnetic Memory; The Floppy Disk and Hard Disk– Hard Disk

• not removable

• rigid platters

• sealed unit

• several two-sided platters

• one read/write head for each platter surface

• thousands of rpms

• Gigabytes of storage capacityWilliam KleitzDigital Electronics with VHDL, Quartus® II Version




• Magnetic Memory; The Floppy Disk and Hard Disk– Hard Disk

• controlled internal environment

• bits closely packed

• concentric circles called tracks (cylinders)

• 20,000 tracks per inch

• 300K bits per inch on each track

• transfer rates of 30 MB/secWilliam KleitzDigital Electronics with VHDL, Quartus® II Version




• Magnetic Memory; The Floppy Disk and Hard Disk– Removable Hard Disks

• Zip disk– 300 rpm

– 100 MB

• Jaz cartridge– two rigid platters

– 2 GB





• Optical Memory– CD

• not as fast as hard disks

• removable

• 650 MB

• aluminum alloy coating

• rigid polycarbonate wafer

• pits = 1 lands = 0





• Optical Memory– CD

• one track starting at center and spiraling outward

• 16,000 tracks per inch

• thin plastic coating to protect

• land reflects light, pit does not

– CD-R• photosensitive dye on reflective gold layer

• laser super heats spot and it will not reflect

• cannot be erased or re-writtenWilliam KleitzDigital Electronics with VHDL, Quartus® II Version




• Optical Memory– CD-RW

• silver alloy crystalline structure

• laser superheats to amorphous state (non-reflective)

• laser can reheat at lower level to turn back into crystalline state

• reflective and non-reflective areas




Summary

• A simple 16-byte memory circuit can be constructed from 15\6 octal D flip-flops and a decoder. This circuit would have 16 memory locations (addresses) selectable by the decoder, with 1 byte (8 bits) of data at each location.




Summary

• Static RAM (random-access memory) ICs are also called read/write memory. They are used for the temporary storage of data and program instructions in microprocessor-based systems.




Summary

• A typical RAM IC is the 2114A. It is organized as 1K x 4, which means that it has 1K locations, with 4 bits of data at each location. (1K is actually an abbreviation for 1024.) An example of a higher-density RAM IC is the 6206, which is organized as 32K x 8.




Summary

• Dynamic RAMs are less expensive per bit and have a much higher density than static RAMs. Their basic storage element is an internal capacitor at each memory cell. External circuitry is required to refresh the charge on all capacitors every 2 ms or less.




Summary

• Dynamic RAMs generally multiplex their address bus. This mean that the high-order address bits share the same pins as the low-order address bits. They are demultiplexed by the RAS and CAS (Row Address Strobe and Column Address Strobe) control signals.




Summary

• Read-only memory (ROM) is used to store data on a permanent basis. It is nonvolatile, which means that it does not lose its memory contents when power is removed.




Summary

• Three common ROMs are (1) the mask ROM, which is programmed once by a masking process by the manufacturer; (2) the fusible-link programmable ROM (PROM), which is programmed once by the user; and (3) the erasable-programmable ROM (EPROM), which is programmable and UV-erasable by the user.




Summary• Memory expansion in microprocessor

systems is accomplished by using octal or hexadecimal decoders as address decoders to select the appropriate memory IC.

• The Electrically-Erasable PROM (EEPROM) and Flash memory use a floating-gate MOSFET for their primary storage element. A charge on the floating gate represents the stored data.




Summary• Magnetic storage like the floppy or hard

disk use magnetized particles to represent the stored 1 or 0. Individual data bits are read and written using an electro-magnetic read/write head.

• Optical memory like the CD or DVD use a laser beam to reflect light off of a rigid platter. The CD or DVD platter will either have a non-reflective pit to represent a 1 or a non-pit (land) to represent a 0.




chapter 16 semiconductor, magnetic and optical memory william kleitz digital electronics with vhdl,...

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