Limits of PALs
PALs have limited resources for implementing combinational logic
- inputs and outputs are limited
- number of product terms per output are limited
Change output polarity
- the complement of a function may use fewer product terms
Implement multi-level logic
- split the logic into parts that can be built piece-by-piece
- try to find meaningful sub-expressions so that specification can
Re-encode inputs
- use common sub-expressions in equations that generate more product terms, e.g., A+B in (A+B)CD
Re-encode outputs
- look for an output (A) that dominates another (B)
- use both to re-construct the one that is dominant, e.g., A = A* + B (dominant defined as always true when the other is true)