· PLA consists of n inputs, m (OR gate) outputs, K (AND gate) product terms and m sum terms.
· The PAL is the opposite of the ROM, having a programmable set of ANDs combined with fixed ORs.
· Compared to a ROM and a PAL, a PLA is the most flexible having a programmable set of ANDs combined with a programmable set of ORs.
o A PLA can have large N and M permitting implementation of equations that are impractical for a ROM (because of the number of inputs, N, required
o A PLA has all of its product terms connectable to all outputs, overcoming the problem of the limited inputs to the PAL Ors
o Some PLAs have outputs that can be complemented, adding POS functions
o Often, the product term count limits the application of a PLA.
o Two-level multiple-output optimization is required to reduce the number of product terms in an implementation, helping to fit it into a PLA.
o Multi-level circuit capability available in PAL not available in PLA. PLA requires external connections to do multi-level circuits.
3-input, 3-output PLA with 4 product terms.