1. Semiconductor, Magnetic and Optical Memory
Chapter 16
Semiconductor, Magnetic and Optical Memory
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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2. Memory Concepts Memory locations have memory addresses
Data are the memory contents
8 bits known as a byte
See Figure Logic Diagram
See Figure Timing Requirements
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3. Figure 16-2
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4. Figure 16-3
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5. 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 Dynamic
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6. Static RAMs Static Dynamic use flip-flops as basic storage elements
use capacitors as basic storage elements
need additional refresh circuitry
can be densely packed
lower cost per bit
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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7. 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 columns
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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8. 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
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9. Figure 16-6
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10. Static RAMs Memory Expansion
using multiple chips to get more memory capacity
See Figure eight 4K chips
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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11. Figure 16-7
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12. 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 cycle
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13. Dynamic RAMs Refresh cycle timing Dynamic RAM Controllers
usually every 2 ms or sooner
Dynamic RAM Controllers
developed to simplify the tasks
Intel 3243
See Figure 16-12
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14. Figure 16-12
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15. Read-Only Memories Store data on a permanent basis Nonvolatile EPROM
erasable-programmable-read-only memory
Stores
operating systems
table look-ups
language compilers
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16. Read-Only Memories Mask ROMs Fusible-Link PROMs
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
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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17. Read-Only Memories EPROMs EEPROMs 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
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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18. Read-Only Memories Flash Memory Floating-gate MOSFET used
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 met
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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19. Read-Only Memories See Table 16-4 See Figure 16-19
Summary of Semiconductor Memory
See Figure 16-19
read cycle
write cycle
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20. William Kleitz Digital Electronics with VHDL, Quartus® II Version
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21. Figure 16-19
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22. Memory Expansion and Address Decoding Applications
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
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23. Figure 16-20
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24. William Kleitz Digital Electronics with VHDL, Quartus® II Version
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25. William Kleitz Digital Electronics with VHDL, Quartus® II Version
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26. Figure 16-23
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27. 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
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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28. Magnetic and Optical Storage
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
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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29. Magnetic and Optical Storage
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 capacity
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30. Magnetic and Optical Storage
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/sec
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31. Magnetic and Optical Storage
Magnetic Memory; The Floppy Disk and Hard Disk
Removable Hard Disks
Zip disk
300 rpm
100 MB
Jaz cartridge
two rigid platters
2 GB
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32. Magnetic and Optical Storage
Optical Memory CD
not as fast as hard disks
removable
650 MB
aluminum alloy coating
rigid polycarbonate wafer
pits = lands = 0
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33. Magnetic and Optical Storage
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-written
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34. Magnetic and Optical Storage
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
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35. 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.
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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36. 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.
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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37. 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.
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38. 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.
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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39. 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.
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40. 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.
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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41. 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.
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42. 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.
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43. 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.
William Kleitz Digital Electronics with VHDL, Quartus® II Version
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