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

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

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

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

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

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

Memory Concepts (Figure 16-3) 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

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

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

2147H Static MOS RAM Read cycle waveforms 12

2147 H Static MOS RAM Write cycle waveforms 13

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

Dynamic RAMs Simplified DRAM read and write operation 16

Dynamic RAMs Usually multiplex address lines Capacitor refreshed during refresh cycle 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 000 0000 RAS is pulsed LOW Increment the A0 to A6 row address by 1 Repeat 3 and 4 until all 128 rows accessed 18

Dynamic RAMs Dynamic RAM Controllers Simplify demultiplexing and refreshing Intel 3242 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

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

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

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

Read-Only Memories 24

Read-Only Memories 2716 EPROM read cycle 25

Read-Only Memories 2716 EPROM program cycle 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

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

Application 16-1 Prom Lookup Table 29

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Application 2 Digital LCD Thermometer 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

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

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

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

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

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 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

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

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

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

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

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

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

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

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

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

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