Regular Structure for Two-Level Combinational Logic
ROM – full AND plane, general OR plane
- cheap (high-volume component)
- can implement any function of n inputs (but double size for one more)
- medium speed
- no optimization needed
PLA – programmable AND and OR planes
- most expensive (most complex in design)
- can implement any function up to a product term limit
- slow (two programmable planes)
- minimize number of terms for outputs together (share terms)
PAL – programmable AND plane, fixed OR plane
- intermediate cost
- can implement functions limited by number of terms
- high speed (only one programmable plane)
- minimize number of terms for each output separately