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Understanding Random-Access Memory in Digital Logic Design

Explore the concepts of RAM, ROM, and programmable logic devices in digital logic design. Learn about data storage, address locations, memory decoding, and various types of ROMs like PROM, EPROM, and EEPROM. Understand the operation of Programmable Logic Devices (PLDs) like PLAs and PALs, with examples and simplifications of boolean functions. Dive into sequential programmable logic devices and basic macrocell logic in this educational chapter.

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Understanding Random-Access Memory in Digital Logic Design

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  1. Chapter 7: Digital Logic Design

  2. Random-Access Memory (RAM) • Data Storage (Volatile) • Locations (Address) • Byte or Word Data input Memory unit 16 x 8 Address Read Write Data output

  3. Random-Access Memory (RAM) • Data Storage (Volatile) • Locations (Address) • Byte or Word m Data input Memory unit 2k x m k Address Read 10 Address lines 1024 locations = 1 K Write m Data output

  4. BC Memory Decoding • Memory Cell Select Output Input Read/Write

  5. Input Data 0 I1 AddressLines BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC I0 1 2 x 4Decoder 2 MemoryEnable E 3 Read/Write Output Data Memory Decoding • Memory Array

  6. Read-Only Memory (ROM) ROM 2k x m k Address Memory Enable m Data output

  7. Read-Only Memory (ROM) Conventional Symbol Array Logic Symbol

  8. Read-Only Memory (ROM) • 8 x 4 ROM 3 x 8Decoder 0 1 2 I2 3 AddressLines I1 4 I0 5 6 MemoryEnable E 7 Output Data

  9. Read-Only Memory (ROM) 3 x 8Decoder • 8 x 4 ROM 0 1 0 0 0 0 2 11 0 1 A2 I2 3 0 0 11 A1 I1 4 1 0 0 0 A0 I0 5 1111 6 1 0 0 1 E 1 7 0 111 0 0 0 0 D3 D2 D1 D0

  10. Types of ROMs • Mask Programmed ROM • Programmed during manufacturing • Programmable Read-Only Memory (PROM) • Blow out fuses to produce ‘0’ • Erasable Programmable ROM (EPROM) • Erase all data by Ultra Violetexposure • Electrically Erasable PROM (EEPROM) • Erase the required data using an electrical signal

  11. Programmable Logic Device (PLD) • Boolean Functions: • Sums-of-Products • AND-plane followed by OR-plane

  12. Fixed AND array (Decoder) Programmable AND array Programmable AND array Programmable OR array Fixed OR array Programmable OR array Inputs Inputs Inputs Outputs Outputs Outputs Programmable Logic Device (PLD) • PROM • PAL • PLA

  13. Programmable Array Logic (PAL) Example w(A,B,C,D)= ∑(2,12,13) x(A,B,C,D)= ∑(7,8,9,10,11,12,13,14,15) y(A,B,C,D)= ∑(0,2,3,4,5,6,7,8,10,11,15) z(A,B,C,D)= ∑(1,2,8,12,13) Simplify: w =ABC’ + A’B’CD’ x =A + BCD y =A’B + CD + B’D’ z =ABC’+ A’B’CD’ + AC’D’ + A’B’C’D = w + AC’D’+ A’B’C’D w A x B y C z D

  14. Programmable Logic Array (PLA) A B C Example: F1=AB’ + AC + A’BC’ F2=(AC + BC)’

  15. Sequential Programmable Logic Device • Basic Macrocell Logic

  16. Homework • Mano • Chapter 7 • 7-1 • 7-2 • 7-3 • 7-18 • 7-19

  17. Homework

  18. Homework

  19. Homework

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