1. Semiconductor, Magnetic and Optical Memory
Chapter 16
Semiconductor, Magnetic and Optical Memory 1

2. 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 manufacturer’s data manual for reading ro writing to a memory IC.
Discuss the operation and application for the various types of semiconductor memory ICs. 2

3. 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. 3

4. 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 4

5. Memory Concepts
Logic Diagram for a circuit to implement a 16-bit memory 5

6. 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 7

7. Memory Concepts (Figure 16-3)8

8. 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 9

9. Static RAMs Static Dynamic Flip-flops as basic storage elements
Capacitors as basic storage elements
Requires additional refresh circuitry
Can be densely packed
Low cost per bit 10

10. 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 11

11. 2147H Static MOS RAM
Read cycle waveforms 12

12. 2147 H Static MOS RAM
Write cycle waveforms 13

13. Static RAMs
Memory Expansion: Using multiple chips to get more memory capacity
Eight 4K chips 14

14. 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 15

15. Dynamic RAMs
Simplified DRAM read and write operation 16

16. Dynamic RAMs Usually multiplex address lines
Capacitor refreshed during refresh cycle 17

17. 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
RAS is pulsed LOW
Increment the A0 to A6 row address by 1
Repeat 3 and 4 until all 128 rows accessed 18

18. Dynamic RAMs Dynamic RAM Controllers
Simplify demultiplexing and refreshing
Intel 3242 19

19. 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 20

20. 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 (microprocessor development system) 21

21. Read-Only Memories EPROMs EEPROMs 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 22

22. 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 23

23. Read-Only Memories 24

24. Read-Only Memories
2716 EPROM read cycle 25

25. Read-Only Memories
2716 EPROM program cycle 26

26. Memory Expansion and Address Decoding Applications
To identify which IC is to be read or written to
Address decoding scheme 16k-byte EPROM (4 x 4k) 27

27. Memory Expansion and Address Decoding Applications
A PROM Look-Up Table
See Application 16-1
A Digital LCD Thermometer
See Application 16-2 28

28. Application 16-1 Prom Lookup Table29

29. 30

30. Application 2 Digital LCD Thermometer31

31. 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 32

32. 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 33

33. 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 34

34. 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 35

35. 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 36

36. 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 37

37. 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 38

38. 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 39

39. 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. 40

40. 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. 41

41. 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. 42

42. 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. 43

43. 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. 44

44. 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. 45

45. 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. 46

46. 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. 47

47. 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. 48