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Field-programmable logic devices

Field-programmable logic devices. FPLA circuits Packaged PLA components with a fuse at every diode in both the AND and OR sections, that can be configured by the user. FPLA. Philips PLS100 FPLA. FPLA. Realizing functions f 1 , f 2 and f 3 with Philips PLS100 FPLA.

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Field-programmable logic devices

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  1. Field-programmable logic devices • FPLA circuits • Packaged PLA components with a fuse at every diode in both the AND and OR sections, that can be configured by the user

  2. FPLA • Philips PLS100 FPLA

  3. FPLA • Realizing functions f1, f2 and f3 with Philips PLS100 FPLA

  4. Programmable Read-Only Memory PROM: fixed AND array and programmable OR array Generates all minterms Can realize k functions

  5. Programmable Read-Only Memory One can directly implement a SOP expression from its minterms using a PROM Is minimization useful with a PROM?

  6. Programmable Read-Only Memory • The AND array provides all 2n minterms • i.e. equivalent to n  2n decoder • Typically no polarity/feedback options • No advantage in minimizing the logic function when using a PROM • Effective for applications that require most minterms to be used • Code converters • Decoders • Lookup tables

  7. PROM application • Gray code generator using a PROM • 15 out of the 16 minterms are used in at least one output (which minterm is not used?) • Therefore, a PROM is not a “waste” for this problem

  8. PROM application

  9. PROM application • Lookup tables

  10. PROM application • Lookup table usage example

  11. PROM application • Multiplier implementation using PROMs • PROMs 1 to 4 are multipliers

  12. Multiplier elucidation An-1…n/2 An/2…0 n bits  low high n/2 bits X n bits + n+1 bits 3n/2 bits 3n/2 bits 2n bits = 3n/2 + n/2 AH AL BH BL W = ALBL X = AHBL U = X + Y Y = ALBH V = Z*2n/2 + WH Z = AHBH T = U + V R = T*2n/2 + WL

  13. PROM application • Read-Only Memory slightly modified

  14. Programmable Array Logic • Fixed OR array, programmable AND array • Limited number of product terms • Product terms cannot be shared • Designer just selects products • More compact and cheaper than a PROM

  15. Programmable Array Logic • Because of fixed OR, the standard representation for PALs is with OR gates

  16. PAL example

  17. ROM technologies • For n inputs and k outputs PROM, what would be the total • Number of diodes? • Number of fuses? • Mask programmed ROM • No user-programmable fuses • Custom mask places wires at fabrication time • Compact and fast • Useful only if sold in large volume, otherwise PROM cheaper

  18. ROM technologies • EPROM - can be erased by UV light and re-programmed • EEPROM - electrically erasable and re-programmable • Both EPROM and EEPROM have relatively short lives: not as permanent as a blown fuse • Complex and slower than ROM • Flexible: can be re-used in iterative design

  19. ROM technologies • Answer: • AND array: 2n2n diodes • OR array: k2n diodes and k2n fuses PROM PAL FPLA Fixed AND OR - Programmable OR AND AND, OR • FPLA: introduced 1975 • Organized ipo • Does FPLA implementation benefit from minimizing “literals”?

  20. PLD design process

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