Semiconductor, Magnetic and Optical Memory

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Chapter 16

• Semiconductor, Magnetic and Optical Memory

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Objectives

• You should be able to
• Explain the basic concepts involved in memory
  addressing and data storage.
• Interpret the specific timing requirements given
  in a manufacturers data manual for reading ro
  writing to a memory IC.
• Discuss the operation and application for the
  various types of semiconductor memory ICs.

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Objectives

• (Continued)
• Design circuitry to facilitate memory expansion.
• Explain the refresh procedure for dynamic RAMs.
• Explain the differences between the various types
  of magnetic and optical storage.

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Memory Concepts

• Memory locations have memory addresses
• Data are the memory contents
• 8 bits known as a byte
• Example layout for sixteen 8-bit memory locations

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Memory Concepts

• Logic Diagram for a circuit to implement a 16-bit
  memory

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Memory Concepts

• Figure 16-3 A typical timing diagram a
  manufacturer might use to show timing parameters
  for a bus driven device
• Data and address lines are grouped together with
  an X to show where they are allowed to change or
  crossover
• Setup time ts
• Propagation delay tp

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Memory Concepts (Figure 16-3)
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Static RAMs

• Random-Access Memory
• Read/Write Memory
• Temporary storage of data (volatile)
• User can access data at any location randomly
• CD player or Hard Disk
• Static or Dynamic

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Static RAMs

• Static
• Flip-flops as basic storage elements
• Dynamic
• Capacitors as basic storage elements
• Requires additional refresh circuitry
• Can be densely packed
• Low cost per bit

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Static RAMs

• The 2147H Static MOS RAM
• 4096 memory locations
• 4k 4 x 1024 4096
• Each location can contain 1 bit
• 4096 unique addresses needs 212 4096 address
  lines
• A0 to A5 identify rows
• A6 to A11 identify columns

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2147H Static MOS RAM

• Read cycle waveforms

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2147 H Static MOS RAM

• Write cycle waveforms

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Static RAMs

• Memory Expansion Using multiple chips to get
  more memory capacity
• Eight 4K chips

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Dynamic RAMs

• Require more support circuitry
• More difficult to use
• Less expensive per bit
• Higher density, smaller size per bit
• Charge is placed on capacitor in each memory
  location

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Dynamic RAMs

• Simplified DRAM read and write operation

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Dynamic RAMs

• Usually multiplex address lines
• Capacitor refreshed during refresh cycle

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Dynamic RAMs

• Refresh cycle timing
• Usually every 2 ms or less
• Three ways to refresh memory cells
• Read cycle
• Write cycle
• RAS-only cycle
• RAS only procedures
• CAS is HIGH
• A0 to A6 are set up with row address 000 0000
• RAS is pulsed LOW
• Increment the A0 to A6 row address by 1
• Repeat 3 and 4 until all 128 rows accessed

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Dynamic RAMs

• Dynamic RAM Controllers
• Simplify demultiplexing and refreshing
• Intel 3242

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Read-Only Memories

• Store data on a permanent basis
• Nonvolatile
• EPROM
• Erasable-programmable-read-only memory
• Useful for storage of
• Operating systems
• Table look-ups
• Language compilers

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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 (microprocessor
  development system)

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Read-Only Memories

• EPROMs
• Can change the memory contents
• Expose an open window to ultraviolet light to
  erase
• Slowest erasure time
• EEPROMs
• Non-volatile
• Erased while in circuit
• Individual bits erased

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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 met

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Read-Only Memories
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Read-Only Memories

• 2716 EPROM read cycle

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Read-Only Memories

• 2716 EPROM program cycle

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Memory Expansion and Address Decoding Applications

• Address Decoding
• To identify which IC is to be read or written to
• Address decoding scheme 16k-byte EPROM (4 x 4k)

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Memory Expansion and Address Decoding Applications

• A PROM Look-Up Table
• See Application 16-1
• A Digital LCD Thermometer
• See Application 16-2

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Application 16-1 Prom Lookup Table
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Application 2Digital LCD Thermometer
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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 with higher
  storage capacities

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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

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Magnetic and Optical Storage

• Magnetic memory The floppy disk and hard disk
• Hard disk
• Not removable
• Rigid platters
• Sealed unit
• Multiple two-sided platters
• One read/write head for each platter surface
• Thousands of rpms
• Gigabytes of storage capacity

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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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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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Magnetic and Optical Storage

• Optical memory
• CD
• Not as fast as hard disks
• Removable
• 650 MB
• Aluminum alloy coating
• Rigid polycarbonate wafer
• Pits 1 Lands 0

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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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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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Summary

• A simple 16-byte memory circuit can be
  constructed from 16 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.

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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.

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Summary

• A typical RAM IC is the 2114A. It is organized
  as 1k ? 4, which means that it has 1k locations,
  with 4 bits of data at each location. (1k is
  actually represents 210 1024.) An example of a
  higher-density RAM IC is the 6206, which is
  organized as 32k ? 8.

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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.

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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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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.

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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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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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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.

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