PPT Slide

3 – Combinational Logic Implementation

© 1996 Gaetano Borriello

Regular logic structures for two-level combinational logic

• ROM – full AND plane, general OR plane

  • cheap (high-volume component)
  • can implement any function of n inputs
  • medium speed

• PAL – programmable AND plane, fixed OR plane

  • intermediate cost
  • can implement functions limited by number of terms
  • high speed (only one programmable plane thatis much smaller than ROM's decoder)

• PLA – programmable AND and OR planes

  • most expensive (most complex in design, need more sophisticated tools)
  • can implement any function up to a product term limit
  • slow (two programmable planes)

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